It's fair to say that Star Trek II: The Wrath of Khan is one of the most beloved films in franchise history. It's the first film in the franchise's history that borrowed elements from the television show to set up its plot. They picked a character who appeared in just one episode to be the main focus of the movie and it worked.
Mostly because that one character, Khan Noonien Singh, was played by Ricardo Montalban, who made it his personal mission to eat up as much of the set as possible with his acting. His portrayal of Khan stands out some 40 years later as one of the best villainous roles ever. Even more so than his first stint in the original series episode "Space Seed".
And yet, not every critic loved it. Slash Films found a host of old reviews of Star Trek II: The Wrath of Khan, and some of them are downright rude. But, did any of them actually have a point about the film?
"When you see stuff like this you wonder if the movies haven't died and someone simply forgot to bury them. A film based on a TV series is a hopeless, self-defeating idea. What people loved about the material on TV is obviously what they're eager to see onscreen, so the director has his hands tied from the beginning. If the movie had any energy of its own — if it looked and sounded like a movie — the audience would probably feel betrayed.- David Denby
"The dull thud of Nicholas Meyer's direction, which mized the custardy platitudes of the original television series with some of the less thunderous special effects of latter-day cinema, has everything in place, like a tidy housewife's kitchen. And the dollars are rolling in to prove we are all children at heart and wish to remain so."- Derek Malcolm
"If only director Nicholas Meyer had grasped the implications of his tale more fully and enthusiastically, this might have become a classic piece of cornball SF poetry, but as it stands the tepid acting and one-set claustrophobia take a heavy toll."- David Kehr
"Foregoing the special effects bonanza of its predecessor, it settles for low camp humanoid melodrama. The aging Shatner and his equally self-amused Enterprise cohorts now 'boldly go' wreathed in soft focus, smiling down on a shipful of apprentice Trekkies. [...] The net effect, between embarrassed guffaws, is incredulity: a movie at once post-TV and pre-D.W. Griffith."- Paul Taylor
If you take out the insults and the need to sound self-important, they're all right at their basic corp. The film is an extended version of a Star Trek episode. That is exactly what The Wrath of Khan is; but what they fail to realize, is that Star Trek is a better self-contained storyteller than most major motion pictures of any era.
The reason Star Trek works on television is the same reason why it should work in theaters; it's a self-contained story that pits the most earnest of emotions against the audience and asks us to decide which person is right when there really, truly is no "wrong" answer.
It forces us to weigh our own beliefs against what is right and wrong, and when Star Trek does that well, there's little in the way of entertainment that can match it and Wrath of Khan did that in spades. While they got the general gist rights (fans loved it for its episodic value), the vitriol was unneeded and counterproductive. It felt like they were attacking hard-working, paying moviegoers and that just comes off as condescending.