Okay, so now I've seen every single Star Trek movie in the course of two days. Brain overload. I'd seen three before (Khan, Generations, the preboot), so this is what I've learned.
1) The even-numbered films are generally more fun and generally more slight. Khan and Nemesis deal with villains out for revenge. Voyage Home plays its story dominantly as a culture clash. First Contact alternates between zombie filmmaking, body-snatchery, and time-travel adventuring, its emphasis chiefly on fast-paced thrills and laughs. Undiscovered Country softens its allegorical edges with an old-fashioned whodunit.
2) The odd-numbered films try to place religious concepts in sci-fi premises. The Motion Picture and The Final Frontier are about quests for God. The Search for Spock begins on an Eden and ends with an ornate ritual (sacrament?) that culminates in a resurrection. Generations reworks Heaven as an aberration in space and time. Even Insurrection deals with a culture of near-immortals living in a paradise of sorts. The cool thing is how these ideas (and their implementation in this genre) recall Clarke's famous line: any sufficiently advanced technology is indistinguishable from magic. It allows the series to wrap transcendent ideas in explicable packages. Savvy, to say the least.
3) The general tenor of the series alternates between hard sci-fi and Buck Rogers fantasy. The opposite ends lie where we are right now, with The Motion Picture as a portentous tale that purposefully emphasizes the Earthly quest for knowledge as nearly divine...and the preboot focusing exclusively on quick-cut shoot-outs and the rapid assembly of its cast for an iconographic finish that functions less as a conclusion than a promise that better adventures will follow. The film that best unites these two approaches is Undiscovered Country, since it offers both a fun murder mystery and a political story about acceptance and forgiveness.
4) Khan, Search for Spock, and The Voyage Home have a nice continuity between them. On its own, I don't think Search for Spock would be worth much, but it's a vital link and helps restore the series to status quo after the disruptive Khan.
5) Insurrection deals with a villain who wants to displace six hundred near-immortals so he can have the secret for immortality. The stakes, however, feel very low, because the near-immortals only risk...displacement. The film would be twice as good if the villain wanted to abduct them all and conduct grotesque experiments to "discover" the secret of life (as well as punish them for having what he hasn't). This idea has precedence, as he and his followers look like science experiments themselves.
6) Tom Hardy makes Nemesis better than Insurrection. Otherwise, the weaknesses (bad character development, limp first acts, too much swashbuckling) are remarkably similar.
7) Final Frontier is not for lack of ambition. But it is for lack of focus. It splatters William Shatner's neuroses and passions all over the screen and leaves us to sort it into a meaningful statement. I think that statement is this: Shatner likes the woods, loves riding horses, and isn't afraid of a little thing like God.
8) Generations is slightly better than I remember, and that comes from Stewart's Picard and McDowell's Soran, who play their roles with more gravity and passion than the story really earns.
9) When I watched the preboot for the first time, I thought it was unfortunate that Uhura had nothing to do. My assumption was that she had more to do in the older films. My assumption was wrong. She does nothing. What a shame. There's a somewhat embarrassing boys' club mentality to all these films, with women on the Enterprise almost never impacting the action or story in interesting ways. That job's left to one-offs like Catherine Hicks in Voyage Home, Kim Cattrall in Undiscovered Country, and, best of all, Alice Krige as the Borg Queen in First Contact. Oh my.
10) Abrams's camerawork clashes so severely with the otherwise stately photography used in the previous films (excluding Frontier's continual camera tracking) that I had trouble watching at times. Lens flares, yes, but also the overabundance of shaky-cam.
11) I would rank them...
Voyage Home
Wrath of Khan
First Contact
Star Trek
The Undiscovered Country
The Motion Picture
Generations
The Search for Spock
Nemesis
Insurrection
The Final Frontier
Those last three are actively bad. The rest range from near-great to good. None of these movies earned my love, but more than enough of them earned my respect. This is an honorable series.