Starting with ST2:TWOK, more attention was given to the FICTION than to the SCIENCE. Let's get it straight: In Sci-Fi, the Sci comes before the Fi. The next two films followed ST2's poor example.
To start off, let's get one thing perfectly clear. Impulse speed is fast. One quarter the speed of light according to accepted sources. That's 46,500 mi.per sec. Even one quarter impulse speed is fast (11,625 mi.per sec.). That's faster than any vehicle known as yet. So why, OH WHY, do Enterprise and Reliant in the nebula scene of ST2 crawl past eachother at such speed?! The audience should have seen the ships blur past eachother. Yes, Impulse speed has been treated quite shoddily in Star Trek. In ST3:TSFS, you will see Kirk order Sulu to proceed out of Spacedock at quarter impulse speed! Hmmmm.....will Enterprise, [a]blast Spacedock with radiation and exhaust from the engines? or [b]go speeeeeding through Spacedock and reduce itself to spacemush to be scraped off the dock walls? Amazingly, it chooses option [c], and, with two aft - facing impulse engines, slowly backs up! That Sulu sure is some navigator, let me tell ya!
And how about those weapons and shields systems. Recall the TOS episode where Enterprise vaporizes an unshielded klingon vessel with only phasers.
In ST2, Enterprise and Reliant exchange phaser fire - without shields - and do little more than crisp their paint jobs and fry Peter Preston.
About Spock, if Genesis had rejuvinated his body, it is absurd that he would lose the bulk of his body mass to become a child. As Maurice Molyneaux probes in his work,
You Will Not Believe a Starship Can Fly, "where did [Spock's body mass] go, and how did he get it back when aging? I didn't see him eating any trees..."
Even the way Spock died perturbed me. Are you telling me that in a starship engineering deck, there was not a radiation protective suit to be found? Pallleeese.
A reference was made earlier to the stupidity of the crew of the former Grissom. But this was quite humorous compared to Kruge's folly. The 'scan' button on the klingon dashboard seems to be as elusive as the Starfleet 'shields' button. Or maybe the klingons just didn't want to bother to scan Enterprise and see there was only five lousy guys in Kirk's "gallant crew." I suppose half a dozen guys or so really is a threat, after all though. Kirk DID blow up his Enterprise just to take out six crummy klingons!
Yes Star Trek 2 and 3 were not as well thought out as ST:TMP. But these are only Freudian slips compared to ST4:TVH.
The first thing that I noticed about Star Trek 4: The Voyage Home that really bugged me was the S.S. Bounty. For a few good reasons. First, the size. It may be my imagination, but that
ship was alot larger in ST3. This wouldn't be the first size-changing ship, though. Recall how big Excelsior was in ST3, compared to Enterprise. Recall that Excelsior was was much too wide to get out
the same doors Enterprise did. Recall how Excelsior squeezed through those doors, anyway. Second, that klingon bridge just isn't the same one used in ST3. Why would the Vulcans refit a klingon vessel?
Third: Vulcan is a prominent member of the United Federation of Planets. Why would there be no starships assigned to Vulcan that could transport Kirk + co. to Earth sooner? If Vulcan has zero starships patrolling
her, than God help those pointed eared morons in case of a Romulan invasion.
The major fault in ST4 was lack of thought on the part of Admiral/Captain Kirk. Kirk was somewhat of a history buff. Didn't he remember the Cold War? Why send a Russian to look for a nuclear vessel?
And most of all, what about Gillian Tailor? Was she an important figure in the future Kirk was trying to save? What about her kids/grandkids/great grandkids/et cetera? Jimmy boy, you didn't even think!
I won't even get into the paradox Scotty may have created with Transparent Aluminum, but you get the picture.