On a whim, I watched Star Trek II: The Wrath of Khan and Star Trek III: The Search for Spock yesterday, for what must have been the first time in twenty-five years.
With the caveat that I am not a Star Trek fanatic (although I do have fond memories of watching repeats of the original series with my father and TNG when a teenager), I have to say that I found the both films (effectively one film) very enjoyable.
Notes:
There was far less techno-babble than features in later series. The audience doesn't need to know how the Genesis project works in great and semi-plausible detail to grasp its narrative role. I found that I didn't miss the expanded explanations one jot.
I was very surprised to find that I felt extremely well-disposed to the principal crew, most of all the Kirk-Spock-Bones triumvirate. Although I first watched these films in the 80s (on TV, not at the cinema), I was quite young, and so I assumed before this re-watch that I'd feel more warmly towards Picard's crew, as they had been my generational-incarnation, the ones I'd watched on first release and soaked in weekly. Well, I think I was mistaken. Spock's death and Kirk's reactions were genuine 'lump in the throat' events, and the interactions between all the main characters seemed utterly convincing (great work given the antagonism that we know existed between some of the actors).
The films have elements that date them beyond the special effects, but I found that these retro-futuristic elements were quite endearing. Even the low-level sexism that crops up here and there seemed to be presented in a way that suggested that those who were susceptible not mean, just daft, and ultimately growing old and headed the way of the dodo anyway.
Religion, faith, belief: they didn't feel heavy or ponderous, but this is deep stuff dealt with deftly. It's mostly covered implicitly, but the subtexts are writ large for anybody who cares to read. It's hard to put my finger on the tonal shift exactly, but the later Star Trek series I have watched seem to be more... clear-cut. Although there's much talk of moral dilemmas and ethical decisions, the 'right' thing to do is usually generally pretty apparent to all but the hard-of-thinking, and we usually end up with the neatly tied bow of having done the right thing, applied the right principles and generated a happy ending. With these two films, I had the sense that the characters had come through their experiences changed (if not scarred) by them, and that the emotions were not simply shed once the mission was over.