Last time I watched some Trek films, I experienced a major change in how I saw one of them, at least. Suddenly, Generations shot from about 2/3 of the way down the list straight to #1 for me. I now think the problem was that it succeeds as adult drama, that can be appreciated better when older, while it "failed" as a popcorn movie, which is basically what Trek films, as opposed to Trek on TV, are for.
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Wrath of Khan is still up there, but the lazy acting has already set in, the cliché lightweight fan-satisfying lines... It works because so much of WoK comes from an effort to do a good film independently of the Trek aspect. We get jarring horror moments, for one thing. And the Trek aspect is there, even if a lightweight version. WoK seemed to be half real Trek, half Star Wars (because of the IL&M effects), an improvement over TMP having been half 2001, half star Wars. 2001 is my favorite film, and TMP did a painfully empty and light version of it. I couldn't believe it, seeing it in 1979. The whole film seemed to be sleepwalking.