Back to TMP, the biggest problem for me was always that there are character arcs and potential character arcs, but, Spock's aside, none of them amount to anything. As I've pointed out in the past, they set up this terrific conflict between Kirk and Decker, and then utterly fail to use it. Decker just gradually becomes Kirk's buddy, even calling him "Jim", but there's no event that causes this shift. I've often felt that a parallel between Spock's story and Kirk's was there, but undeveloped: namely, both men are obsessed with finding their place, and both are taking enormous—perhaps suicidal—risks to get what they need. Kirk's pushing to be the Captain, at the possible risk of his crew and every living thing on Earth. But Kirk's conflict just evaporates. I've often felt Spock's spacewalk should have been Kirk's wake-up moment, wherein he recognizes that his own behavior is as obsessive as Spock's, and he finally starts acting for the mission instead of himself, and, in doing so, rediscovers the person he is. It wouldn't have taken much—mostly dialog tweaks, but the idea obviously didn't occur to the writers. Too bad.