Star Trek III: The Search for Spock

Essential as the middle of three. Watch Khan immediately before it: this film opens in the last scene of that one and resolves its ending, so it is unintelligible on its own and anticlimactic with a gap.

It is also the least regarded of the three and the case against it is mostly that it undoes something. The previous film's ending was the most affecting moment in the franchise, and this one spends a hundred and five minutes walking it back, which is a structural concession to an actor who had changed his mind. Leonard Nimoy directed it, which is the joke that writes itself and is also why the film is more interested in the crew than in the mysticism.

What it does well is the cost. Kirk steals a starship, ends his career, and loses something he cannot replace in order to recover a friend, and the film is clear-eyed about the fact that he has traded a great deal for it. The scene where he reacts to a death on the bridge is the best acting William Shatner ever did on film.

Christopher Lloyd's Klingon commander is a thin antagonist and the Genesis planet is a set. Watch it as the second act of a three-film story rather than as a film, and go straight on to The Voyage Home.