2.1 Unit Specifics
2.2 Racial Generalizations
2.3 Racial Specifics
The following table provides functional grouping for most of the units and some structures. The purpose is to identify units and structures according to their purpose or function.
| Terran | Zerg | Protoss | |
| Non-Combat | |||
| Harvesting | SCV | Drone | Probe |
| Repair | SCV | (not applicable) | (innate shield regeneration) |
| Healing | Medic | (innate regeneration) | (none) |
| Ground-to-Ground Combat | |||
| Melee | Firebat | Zergling, Ultralisk | Zealot, Dark Templar |
| Mid-Range | Marine, Ghost, Vulture, Goliath, Tank | Hydralisk, Lurker | Dragoon, Archon |
| Long-Range | Siege Tank, Nuclear Missile | Sunken Colony | Reaver |
| Special | Ghost | Defiler | Templar, Dark Archon |
| Ground-to-Air Combat | |||
| Mid-Range | Marine, Ghost | Hydralisk | Dragoon, Archon |
| Long-Range | Missile Tower, Goliath | Spore Colony | Photon Cannon |
| Special | (none) | (none) | Photon Cannon, Templar, Dark Archon |
| Air-to-Ground Combat | |||
| Mid-Range | Wraith, Battle Cruiser | Mutalisk | Scout |
| Long-Range | Battle Cruiser | Guardian | Carrier |
| Special | Science Vessel | Scourge | Arbiter |
Mobility influences greatly or perhaps even determines strategy and tactics. For example, hit and run tactics are effective only with very fast units. Marshalling troops at a staging area is greatly complicated by dissimilar movement rates. And area-effect weapons (e.g., psi-storm) or area-effect special abilities (e.g., EMP shock wave) are far more effective against units less capable of avoiding them through movement.
Zerg is the most mobile race followed by Protoss and then Terran. The only genuinely slow units possessed by the Zerg are guardians; overlords and ultralisks are initially not very mobile, but their respective upgrades fix this. As noted elsewhere, Zerg is also the only race capable of moving ground troops across any distance near-instantaneously, courtesy of their nydus canals.
Protoss are more mobile than Terrans for several reasons. While reavers and templar are both relatively slow, the Protoss have the second-fastest ground unit (zealots), the fastest transport (shuttles), and the fastest air unit (scouts). Protoss units also do not suffer from awkward pauses during which they are entirely vulnerable to attack unlike siege tanks, the very backbone of Terran ground forces, while switching modes.
Finally, Terrans are the most mobility-challenged race of the three. To be effective on offense requires constant pauses on the ground while siege tanks switch modes. Additionally, battle cruisers move very slowly, dropships are not very quick, marines are slow, etc. On defense the situation is even worse; strong Terran defense virtually demands immobile structures like missile turrets and especially bunkers. Speed-upgraded vultures are admittedly the fastest ground unit in the game, but their fragility and limited offensive potential usually offset their speed.
When it comes to cracking tough defenses or making a decisive attack, what often matters most is an ability to hit as hard as possible as fast as possible. Those precious few seconds before the enemy reacts (at least against human opponents) may mean the difference between victory and defeat as can quick destruction of important units/structures. Dealing maximum damage as quickly as possible is thus very important.
Terrans are the clear favorites here. No other weapon in the game has the single-strike power of a Terran nuclear missile. Nuclear missiles are followed closely by what is arguably the second most powerful weapon in the game, namely, the Yamato cannons found on battle cruisers. The initial volley generated by a column of siege tanks as they lock down into siege mode can also be utterly devastating. And finally, the judicious and repeated application of stimpacks to squads of marines and/or firebats surrounded by medics can deal a ridiculous amount of damage very quickly.
Zerg are probably the first runner up in this category. A pack of Zerg guardians can annihilate almost any ground unit (and some structures) with a single volley. A queen is guaranteed to execute almost any single ground unit via the spawn broodling ability. Fully upgraded zerglings are incredibly destructive in the late game, tearing almost any structure down in mere seconds if allowed to run unchecked.
Finally, the Protoss bring up the rear with a notable inability to crack tough defenses quickly. Templar psi-storms stand out as being capable of dealing a great deal of damage in short time, but storms are useless against structures. The addition of the corsair in Brood War is indeed welcome and helps offset this disadvantage. But although corsair disruption webs allow one to nullify the threat from ground units or structures in a given area, it provides only protection; it does nothing to destroy them.
Different units have different strengths and weaknesses. Starcraft would be a boring game indeed if it were possible to build simply one type of unit in order to guarantee a win. Games would be little more than a race to acquire exactly that unit. The more flexible a unit is, however, the better it can be utilized in differing situations and thus the more effective it will presumably be.
Zerg units are quite flexible. Only Zerg have the ability to hide most ground units by burrowing—a tactic very useful for gathering troops at a staging area. Only Zerg have hydralisks, which are fairly inexpensive, relatively tough, quite mobile, fierce in combat (against air or ground forces), can be mutated quickly into lurkers, and seem not to suffer from movement problems with the AI to the same degree as do Terran goliaths or Protoss dragoons. Zerg mutalisks are similarly flexible, capable of mutating into both guardians and devourers as needed. Of course, the Zerg do have their share of rather limited units as well; guardians, zerglings and ultralisks are completely useless against units in the air, scourge and devourers are useless against units on the ground, queens cannot attack at all (save for their spawn broodling ability), etc.
Terran units are almost as flexible as the Zerg. Goliaths, roughly the Terran analogue to hydralisks, are plagued with movement AI problems and are not as effective against ground units. Wraiths, while fairly useful against units in the air, are not effective at all against targets on the ground except in very large numbers or when they may attack with impunity thanks to their cloak. Playing Terran rather than Zerg is harder, in my estimation, insofar as it is necessary throughout all phases of the game to use a diversity of units to achieve one's goals. In the early and middle game, the Zerg can usually dominate with only hydralisks whereas Terran forces must include marines and medics, tanks and quite often firebats, vultures or goliaths to be truly effective.
Finally, Protoss units are probably the least flexible in the game. Reavers, roughly similar to Terran siege tanks, are not limited merely to attacking ground units; they are limited to attacking units accessible on the ground. That is, their scarabs must travel on the ground to their targets before detonating. In the early game, Protoss have only zealots, which are utterly useless against targets in the air. Templar require a great deal of micro-management to be effective. Dark templar are useful only on the ground. Scouts are all-purpose units, but their extreme cost and fragility make them costly to deploy. Dragoons are highly useful against targets on the ground or in the air, but they are plagued with movement AI problems, etc. Finally, more than Zerg and perhaps almost as much as Terran, Protoss require a combination of units to be effective.
Each race has the ability to build certain fixed structures, which may be useful in combat. Terran missile turrets, for example, make fairly quick work of enemy aircraft, Zerg sunken colonies can be devastating, etc. Some are useful only a defensive capacity, others are useful for both offense and defense.
Protoss have the clear advantage in terms of structures. Photon cannons fire quickly, do a fair amount of damage, are relatively tough and fire against targets on the ground or in the air. And unlike Terran or Zerg, Protoss can build pylons and photon cannons almost anywhere on the map. If one has minerals to burn, for example, walling the enemy into his base with pylons and photon cannons can be both effective and amusing. And perhaps most importantly, Protoss can defend multiple bases far easier than Terran or Zerg because of photon cannons.
Zerg have almost as much to celebrate as Protoss. Their sunken colonies are quite powerful, and their spore colonies are deadly to aircraft. But both structures must be built upon the creep, which makes them useful almost solely for defensive purposes. Of course, given the many strengths the Zerg units possess, this is probably a good thing. But it sure would be fun to surround an enemy base with sunken and spore colonies…
Terrans come in dead last with regard to useful structures, as they are almost entirely defensive. Protoss and Zerg both enjoy automated defenses, whereas Terrans have automated defenses against air attacks only. Of course, missile turrets and bunkers can make for a very powerful defense, but they always require troops to be useful, which subtracts from the overall supply limit maximum. In short, it is harder to defend multiple bases as Terran—a fact which can frequently lead to poorly defended expansions.
As in any contest between factions of the same race, victory will be granted either to the better military commander or to the better mechanical player. That is, either superior tactics and strategy will win the day, or the player who is better at the mechanics of the game (i.e., quicker at managing his buildup and production) will win. There are no inherent advantages possessed by either player.
In such a situation, Terran strengths become their weaknesses and vice versa. For example, it is normally a Terran strength that so many of their units are mechanical in nature and can be repaired, but their being mechanical also leaves them open to being locked down by ghosts. Similarly, whereas siege tanks normally inspire confidence in their defensive power, they suddenly inspire terror in opponents for their ability to destroy defenses with impunity from extreme range. Further, the ability of various units to cloak is normally a powerful asset, but against an opponent with comsats, these units become far less useful. In short, Terran vs. Terran can be very challenging. Nevertheless, there are some important areas that remain available for leverage.
For starters, use ghosts! Against Terrans, ghosts are extremely powerful—particularly in the field. Remember that science vessels are expensive; as such, they are often not brought along with attack groups. In such cases, ghosts can easily lock down siege tanks, battle cruisers, etc. in order to sway the balance of power. Further, if one's opponent is careless enough to leave his marines un-bunkered, cloaked ghosts can quickly dispatch them—possibly before comsats can be brought to bear. If one finds a orce too large to be dealt with in such a stealthy fashion, simply bring up a cloaked ghost and call down a nuclear strike. Ghosts are very important in Terran vs. Terran matches.
Despite the relatively diminished value of cloaking, build wraiths instead of (or at least instead of some) battle cruisers. Battle cruisers are useful, but they easily locked down by ghosts. One's highly expensive and deadly battle cruisers can quickly become nothing more than large practice targets with ghosts in the area. But wraiths, since at least twice as many may be built for the same resources, can be far more numerous. They are thus much harder to lock down. Further, if one's enemy ignores this advice and goes for battle cruisers, large packs of wraiths make very short work of them. Remember also that science vessels are expensive and comsats have a limited amount of power available; once the enemy's means of detection is destroyed or compromised, one's wraiths can attack with impunity.
The Brood War expansion makes three additional comments necessary. First as regards science vessels, their expense is greatly decreased in Brood War, and as such, they are brought along in the field far more often than they were previously. Second, comments regarding ghost lockdown should be taken with a grain of salt; the ability of medics to restore locked units should not be underestimated. Third and finally, one will have to balance wraith production against enemy valkyrie production. If one's enemy strives for a fleet of battle cruisers alone, for example, then a couple of packs of wraiths—preferably accompanied by ghost lockdown—will be a sufficient counter. If the enemy builds valkyries, however, then one must build many more wraiths, ensure they may cloak successfully, or provide another counter for the valkyries.
Against Zerg, Terrans have a couple of strengths. The first is their relative strength on the ground in the early game. The Zerg are confined largely to zerglings and hydralisks for a while, and during this time Terran siege tanks can be developed. Assaulting a Zerg base with only a couple of siege tanks and a handful of marines can be brutally effective. Against the Zerg, Terrans can attack in the early game with relatively good chances of doing serious damage. If siege tanks are not yet available, then build bunkers outside the Zerg base and try to shut them in until tanks are available.
If one prefers to hit even earlier, stimmed marines can be devastating. Again, Zerg have only hydralisks and zerglings during the early game while Terrans can easily have developed stimpack technology. A single squad of twelve marines can utterly annihilate scads of zerglings and hydralisks when stimmed. This is far easier to do if the range upgrade is also available, but either way it is a very useful tactic.
In the early game prior to siege tanks, vultures can cause quite a bit of trouble for Zerg opponents. A pack of three or four vultures with the mine upgrade can create a pretty deadly mine field outside a Zerg base. At the very least, it will take a fair amount of time to destroy all the mines via overlords and drones if it doesn't kill a nice number of units instead. It will also tend to make the enemy paranoid while moving troops, which is always a useful thing. And of course, vultures are pretty deadly as straightforward combat units against zerglings and drones.
Cloaking can also be quite useful, but only in certain circumstances. Most Cerebrates neither bring overlords along when attacking in the early game nor build spore colonies until they have proof that wraiths will be a problem. Thus, if one can build a squad of six or more wraiths with the cloaking upgrade, it is frequently possible to destroy Zerg in the field or destroy Zerg expansions using them alone. The wraiths will be needed anyway—if for nothing else to kill the inevitable guardians—and they can be very powerful against Zerg in the field or expansions sans spore colonies and overlords. Further, making one's wraiths known is a great way to force Zerg to build spore colonies, and any resources being spent on spore colonies will not be spent on more mobile units.
A couple of comments regarding Brood War are again appropriate. First, the Zerg are no longer weak on the ground in the early game thanks to improved sunken colonies. But of course, this may be offset due to the introduction of medics; with medics around, Terran marines can be stimmed again and again. And second, the relative merits of cloaking are perhaps somewhat diminished. To survive the Brood War single-player missions, it is usually necessary for overlords to escort one's forces, which forms a bad habit as far as Terran Magistrates are concerned.
The greatest Terran strength against Protoss is their diversity of units. A few of the right kind of force is far more effective than lots of the wrong kind of force. Be sure to mix firebats with marines and have vultures handy as well for the early game. These three together are a deadly combination against zealots. Once dragoons are brought to bear, start building more marines than firebats.
If one does not have this crucial mix of forces available, marines alone can still be effective if the stimpack upgrade has been researched. I learned the value of stimmed marines some time ago, and I have not forgotten. A squad of twelve marines can destroy twelve zealots sans leg upgrades if stimmed. The stimpack upgrade can be so crucial for the early game if used effectively, and this is certainly true against zealots.
One of the Protoss strengths is that their units are useful throughout the entire game; e.g., zealots are as useful at the end as they are at the beginning. The clever Magistrate should recognize this and keep building vultures, since they are, by far, the greatest single threat to zealots in the early game and are still quite useful once advanced units are available. It takes 160 points of damage (80 shield and 80 hit points) to kill a non-upgraded zealot in top condition; a mere eight vultures can deal this damage in a single round of fire. While eight vultures cost enough for twelve marines, it is a force well worth assembling. Additionally, the vultures' great speed allows them to hit and run, luring zealots into traps or just annoying them. And finally, even when under attack by large numbers of zealots, vultures can still do fairly well despite their slow rate of fire because of the area effect of their weapons.
Much like Terran vs. Terran campaigns, ghosts are very useful in Terran vs. Protoss campaigns. Against zealots, they deal serious damage with their rifles. Against dragoons, reavers or any of the other mechanical units ghosts may be used to lock them down. The one caveat here is to be sure to bring detection whenever possible or scan first; Protoss observers are hard to beat for ongoing reconnaissance, and it simply won't do to have one's ghosts discovered.
Toward the end of the middle game, science vessels will become almost crucial. Nothing reduces the Protoss toughness better than dropping their shields through a science vessel's EMP shock wave. A science vessel or two accompanied by a pack of wraiths can also be very effective in hunting enemy observers. Further, science vessels can make small numbers of battle cruisers far tougher via their defensive matrix ability. In short, never forget to build science vessels when fighting Protoss. A single EMP shock wave allows a lone nuke to destroy most Protoss structures—something important to remember when sending a ghost to call down the thunder.
The Zerg's greatest strength as a race lies in its ability to build and expand quickly, and this is certainly no different against Terran opponents. Of course, the Zerg suffer from a defensive disadvantage on the ground in the early game, so it is wise to build carefully and plentifully in terms of base defenses. Otherwise, one can be overrun rather quickly by stimmed marines or siege tanks shortly thereafter.
The key to Zerg victory over Terran opponents is to get an early start. Recognize that zerglings are cheap; recognize also that causing trouble for one's opponents is key in the early game; the natural next step is to recognize that one should send zerglings to confound one's opponent(s) at the earliest possible opportunity. It should be possible to get six zerglings to the enemy base (at least on small maps) roughly about the time a first bunker and a maximum of two marines are ready for defense. If the enemy has built poorly, make use of this opportunity; i.e., kill his SCVs if possible, start destroying something out of the range of his bunker, etc. The hassle doesn't have to be major (although that never hurts); it just has to be annoying enough to cause some damage and delay. Never underestimate the value of psychological damage.
On the other hand, if the enemy has built well, this is even better. Simply stay put; use these zerglings for reconnaissance. Place them such that they can detect his leaving his base and burrow them as soon as possible. Keep sending zerglings and eventually hydralisks to pin the Terran down. He will need siege tanks to break free, and this amount of time allows the smart Cerebrate to expand with impunity. In my experience, the opponent will get too caught up in trying to break free to keep building properly. In this case, it is often possible to come raining down on him with overwhelming force thanks to several expansions bringing in resources. Occasionally, one gets an enemy who is smart enough not to attack until he can be sure of victory. In such a case, either make him pay for it dearly or retreat. In the very worst case, one will still have good information about what sort of forces he has while simultaneously out-expanding him.
Once one's opponent gets siege tanks, it is imperative that one have either overwhelming numbers of zerglings and hydralisks or queens. Otherwise, a scant few siege tanks can spell defeat. The spawn broodling attack is almost indispensable for dealing with tanks, although the ensnare ability is probably more useful generally. If one is able to pester the enemy properly as described earlier, it should be possible already to have queens and the broodling attack. Otherwise, mutalisks can be of great help versus tanks—particularly if the ensnare attack can be used on any of the units escorting said tanks (e.g., marines).
In short, a key to victory as Zerg over Terran is to outrun them in the race to high level units. It is always possible to defeat a weak Terran by overwhelming him simply with hydralisks and zerglings, but a strong Terran will require more advanced units. And in my experience, the best way to secure this sort of victory is to make sure that one has advanced units prior to the enemy gaining technological ground. Large numbers of Terran battle cruisers, for example, can be very difficult to defeat, but if one avoids this problem altogether by getting to guardians first, victory is almost assured. So, keep the enemy bottled in, or at least off balance, while one's own economy expands in order to accommodate climbing the tech tree and producing lots of units. Do this, and the swarm will always be victorious.
Zerg versus Zerg usually makes for short, brutal games. On small maps, the first to get zerglings to the enemy drones often wins. On larger maps, whoever out-expands the other generally wins. With Zerg versus Zerg, it almost always comes down to a sort of brutal success; i.e., winning by utterly out-muscling the enemy. Both sides are equally matched in terms of racial abilities; it is simply a question of which Cerebrate's tactics and (more often) mechanical skills will win the day.
Nevertheless, there are a few notes I have gathered to help defeat opposing breeds of the swarm. First, it is critical to build adequate forces in the early game. If one concentrates too much on economy, one will surely be overrun by enemy zerglings. Once a spawning pool is available, build zerglings as fast as possible, building drones only as minerals allow. If possible, deploy them outside the enemy base; when the enemy sends his own zerglings on the prowl, the units already in position will be easily victorious versus the units streaming individually out from the enemy base. Once at least 24 zerglings are available, one may start working on hydralisks.
Once adequate forces are available, it is necessary to victory to discover what sort of path the enemy is taking. If he has concentrated primarily on economic expansion, simply send all available forces to destroy his base (or preferably his first expansion if possible); he will not have adequate defenses and will lose. If he has built adequate defenses, then again try simply to box him in while expanding with impunity. Victory follows (usually) from out-expanding one's opponent even once. A second stream of revenue (along with enough hatcheries to build units) can win the day.
If a quick win is not possible by either brute force or economic expansion, then my only remaining suggestion is to be sure to build the appropriate special units and use them well. Build at least one queen (preferably more) for parasite-based reconnaissance, ensnaring hydralisks and the broodling attack against ultralisks. Build at least one defiler (preferably more) for the cover of the dark swarm and plague. And in my estimation, it is always useful to build plenty of guardians. For further suggestions, refer to my comments regarding specific units.
The Protoss provide probably the greatest challenge for the Zerg. The Zerg's greatest strength is their fast buildup and ability to expand; this is why they are so effective against the Terrans who get off to a slow start. While it is true that the Protoss get off to a slow start, they are slow only in terms of build time for their units. That is, while Terrans are slow to get devastating units, the very first zealot to step out of a gateway is a serious threat. Thus, while the Zerg can almost always attack the Protoss first, it is a very dicey proposition to overwhelm a good Executor in the early game. A good Executor will have at least three gateways warping zealots very quickly, and that can mean nothing but trouble for the Zerg.
So how, then, do the Zerg win against the Protoss? This will depend largely, I think, upon what route the Executor takes. If one's opponent is building strictly zealots, then build mutalisks and try to get queens for their ensnare attack. If one's opponent is building plenty of dragoons, then build more hydralisks as they always annihilate dragoons and do well against zealots, and try to get queens for their ensnare and broodling attacks. If one's opponent starts building reavers, mutalisks will be necessary, at least until tougher units like ultralisks and guardians can be brought to bear. If one's opponent starts building templar, be sure to keep tabs on them if at all possible. Templar are probably a greater threat than reavers because of their deadly storms, which are effective against targets both on the ground and in the air. The broodling attack is just about the only sure way to handle them.
Winning against the Protoss is difficult. Using ensnare on zealots and scouts can make them much easier to kill. Using guardians against reavers prevents huge losses in terms of ground troops. Using queens against templar is practically necessary. Having ultralisks for destroying reavers and archons is always useful. In summary, the advantages of the Zerg as a race diminish significantly beyond the very early game against the Protoss. The successful Cerebrate will have good reconnaissance and build accordingly.
Not so long ago, I would have said that against Terran opponents, Protoss have significant advantages. But in light of recent lessons I know now that this is clearly not the case. In the early game, one's best strategy may be summed up as follows: (1) never stop building zealots and dragoons and (2) get the leg upgrade as soon as resources permit. The enemy will eventually get wraiths, and it is generally a good idea to build at least two or three photon cannons near the harvesting line, but at first it is enough simply to build zealots and make them fast.
The two greatest threats to Protoss hegemony in the early game are stimmed marines and attack forces that include firebats and vultures. If one is playing against a slow or ignorant opponent, it should be possible to overrun his base with nothing but zealots before he gets firebats in place. If, on the other hand, one's opponent is shrewd, then it would be a good idea to build shield batteries (or photon cannons) near the choke point to one's base; otherwise, one's zealots can get into trouble in a hurry. If one can get four gateways in place warping zealots and dragoons, however, most Terran opponents will not be able to keep pace. Expand quickly and destroy the enemy despite his stimpacks and firebats/vultures.
Beyond the early game, reconnaissance, reavers and templar will be key in defeating the enemy. Park an observer outside the enemy's base. If he seems to be moving troops, then follow him; as soon as the staging area is located, drop reavers or templar from shuttles while zealots move in for the kill. Terrans are weakest when out in the field, so be sure to leverage this fact. Psi-storm his troops while reavers launch scarabs, then send zealots in to mop up whatever might be left (which usually isn't much). When cracking Terran defenses (usually bunkers with siege tanks), send hallucinated zealots into the fray first followed by real zealots, then drop reavers outside the firing range of the bunkered marines. The hallucinated zealots will draw enough fire to allow the real zealots to kill tanks and the reavers to then kill everything else. Load and unload the reavers into and from the shuttle as needed.
Speaking generally, when minerals are plentiful, build zealots, reavers and dragoons. When gas is plentiful, build templar and observers. No matter what path the enemy takes, they will all be useful; what is key is to never stop building and keep close tabs on the enemy. When one has more templar than can be effectively managed, merge them into archons. Expand as possible and prepare to build plenty of air power as soon as circumstances permit.
Toward the late game, Protoss air power will probably be necessary, if not carriers then at least scouts. Have at least some scouts available to kill wraiths. If one is going for scouts, then build as many as possible and upgrade their speed; this allows hit-and-run attacks followed by trips back to shield batteries. If one can build two squadrons of eight to twelve scouts, it should be possible to mow down enemy units with one squadron while the other is busy recharging. These scouts should also allow destruction of enemy wraiths and battle cruisers. Their primary foes are cloaking and ghosts. If one builds carriers, which can be useful for waging serious battles against ground units, then build many. They are relatively useless until at least four are available, so be sure to support them with scouts and ground troops, or they will remain useless as they are destroyed by wraiths or battle cruisers.
Brood War changes the middle and late game for the Protoss somewhat because of the new corsair unit. The corsair's disruption web ability greatly minimizes the number of zealots and dragoons one needs to involve in any ground assault. A handful of corsairs can completely nullify sunken colonies, siege tanks, bunkers, photon cannons-pretty much whatever the enemy might have in the way of solid defenses.
Against Zerg, the only time an Executor need worry is at the beginning of the game. The Zerg start quickly, and unless one warps gateways and zealots quickly, one may be overrun rather easily by even mere zerglings. Be sure to produce enough zealots to defend against a zergling rush and never stop building them. As one's economy permits, warp a second gateway and then a third; warp a fourth and possibly a fifth as well if one is going for the early win. Four to five gateways will almost always spell victory against Zerg in the early game. The key is getting the kind of economy that will support such a thing. Once the leg upgrades are available, send troops to mess with the enemy, or preferably an enemy expansion. While the enemy is busying dying, expand. Even if the attack doesn't end the game or even make a decisive victory, it should buy the time to expand and should reduce Zerg forces enough to expand in relative safety.
Note, however, that zealots alone will not guarantee safety in the early game. I have lost too many times to Zerg players who take to the air all-too early. Mutalisks are fairly powerful air units, and they are available earlier and in greater numbers than it is generally possible for the other races to match for a while. Once one has assembled at least a few zealots, start including dragoons in the build order. Otherwise, one's base may be overrun by mutalisks, and that will spell the end of the game.
If one survives the early game, then beating Zerg is a matter of leveraging Protoss strengths against Zerg weaknesses. Zerg, for example, are fairly weak on the ground, whereas Protoss are not. Relying upon strong zealot ground forces can be very effective. The only serious zealot disadvantage is their vulnerability from the air; thus, if one can provide cover (e.g., using scouts, templar, dragoons, etc.), then zealots alone can win ground conflicts. Once the Zerg have guardians, scouts, dragoons, templar or archons will be needed, but until then Protoss strength on the ground alone can carry the day.
Once all the special units are available, I suggest keeping templar and reavers handy in all circumstances. Reavers can kill dozens and dozens of ground units very quickly while templar can do the same with their storms. I also suggest building scouts to handle the inevitable, deadly squads of guardians.
The Brood War expansion complicates matters somewhat. Since the Zerg may now get lurkers very quickly, it is utterly crucial that one build photon cannons sooner than before. And if one is ever to conduct operations in the field, observers will be similarly necessary. Also, because sunken colonies are so much stronger, leg upgrades and dragoon backup will almost always be necessary to crack early game Zerg defenses. Beyond the early game, corsairs will play a key role in shutting down enemy defenses.
Protoss versus Protoss, much like Zerg versus Zerg, often makes for short, brutal matches. Whoever amasses more zealots, or perhaps uses them more effectively, may frequently bring the game to an end in a big hurry. In light of this, the early game buildup should be focused upon producing as many zealots as possible, bringing dragoons into the picture only if one's opponent goes for shuttles-and even then photon cannons can do much to prevent reaver drops and similar tactics. I cannot emphasize this point enough: focusing on anything other than zealot production can easily spell defeat.
Nevertheless, there is room in the early game for some variation. As always, reconnaissance is key in guiding one's development. If the enemy is going for a zealot rush, then building anything but zealots is suicide. If the enemy is making an early leap up the tech tree, then teach him the error of his ways with a zealot rush. If the enemy is taking a more moderate buildup (e.g., building some dragoons and climbing the tech tree at a "normal" rate), then there is greater freedom. One may try to expand, go for a zealot rush, leap up the tech tree for a reaver drop or templar (NB: this should be done only if adequate defenses are already available), etc.
If one makes it out of the early game intact, then the game is surely to become more interesting. And again reconnaissance will be key. Thus, the first step for the middle game is to build a robotics facility and an observatory. Build a robotics support bay as well if resources easily permit. At least one observer should be constructed and placed in or near the enemy base. I am often surprised by the number of Executors who build observers only against Terrans; leveraging this common mistake can provide excellent, ongoing reconnaissance and can easily be the difference between winning and losing.
At this point, then, strategy blossoms where brute force might previously have sufficed. If the enemy goes for templar (and thus archons), then consider going for air power; scouts with the speed upgrade can generally use hit-and-run tactics so quickly that templar will have trouble throwing their storms in the right place. Alternately, one could switch zealot deployment tactics; e.g., attack from the front with one force (and thus draw the storms) while attacking the rear with another. Also, one may drop reavers near enemy templar and kill them quickly, but this requires rather deft manipulations for proper execution. If, as is more often the case, the enemy goes for reavers and more ground forces, then again air power can be devastating. Scouts can easily destroy reavers, after which zealots can conduct mop-up operations. While dragoons provide an obstacle to this, they can be overcome with zealots. One last observation about Protoss versus Protoss middle game is that it will be necessary to secure at least one or more expansions during this phase. The sort of units needed demand it.
By the late game, a lack of air power will be deadly. One's enemy will almost certainly show up with large groups of scouts or carriers as the former can be devastating with hit-and-run tactics and the latter can be even more devastating if given an opening. Both can be dealt with via dragoons or templar psionic storms, but it is much easier when using air versus air. Similarly, a lack of special units will likely be fatal as will failure to protect them. One's enemy is also likely to show up with shuttles full of reavers, which are best dealt with from the air. Suffice it to say that the late game is usually won on the basis of using air power in conjunction with ground forces and special units. I recognize the relative vagueness in this characterization, but it is simply the best way to put it.
A favorite tactic of mine during the late game is to use hordes of zealots as a ground force with carriers for air support. If the carriers get in trouble, be sure to have at least one arbiter handy elsewhere for its recall ability. Large squads of scouts accompanied by corsairs can also be very effective; use corsair disruption webs to prevent fire from the ground while the scouts destroy everything in the web and the corsairs protect the scouts from air attacks.
In the late game, upgrades are also rather important. By this time, the resources should be available to fully upgrade units on the ground and in the air. This is particularly important if scouts and carriers are a major component of one's forces.
Finally, Protoss have one advantage not shared by the other races, namely, their photon cannons are fairly powerful, fire fairly quickly and can hit targets both on the ground and in the air. As such, it is much easier for Protoss to bypass some of the annoying features of the two-hundred unit supply limit. Whereas Terrans must leave bunkered marines or tanks and Zerg spore/sunken colonies must be built on creep, Protoss cannons can be built anywhere a pylon can be built to power it. This makes it easier to defend bases, easier to choke and opponent's mobility, easier to defend staging areas, easier to have ongoing reconnaissance with some teeth to it, etc. Leverage this ability when possible on offense; always use it on defense.
Brood War makes a couple of additional comments necessary. First, the importance of observers is at least doubled with the addition of dark templar. Without them, a lone dark templar can destroy ground forces with impunity. And second, since reaver drops have been complicated by the addition of a cool down period following emergence from a shuttle, dropping reavers must be managed much more carefully.