TMP: It's my favorite of the Trek films because it was the only Trek film to be majestic, have scale, and be a piece of cinematic art on par with 2001: A Space Odyssey and Metropolis. I could care less if it remade an episode I've never even seen, or that the pace was too slow. It remains one of the few examples of 1970s-80s SF that was and remains truly immersive. I hate 3-D, but I'd actually make an exception for TMP.
WOK: A more intimate film than TMP, with a stronger storyline and a faster pace. But as critics of the day pointed out, this could have just as easily been a made-for-TV movie. That's not saying it's a bad film by any means. But even back in 1982 I saw it as a step down from TMP. Then again, I never expected to see a Star Trek II come out anyway, so I was just happy to have a sequel. And I didn't mind trading majestic flybys of alien ships for Lt. Saavik.
SFS: Christopher Lloyd was cool, and the idea of killing off David was brave, but I never cared for this one. It seemed a "smaller" movie than even WOK, and there were some continuity issues (i.e. the age of the Enterprise) that even I couldn't ignore. I also didn't care for the recasting of Saavik. "Up your shaft" and the ending made up for a lot of it.
TVH: I love this film, which was the first "comedy" Trek film. They needed one after the rather dark events of the first three. Nimoy made up for the dullness of SFS with a story that was and remains quite timeless. I wish they'd stayed with the "Saavik is pregnant with Spock's child" thread instead of pulling a Chuck Cunningham with the character.
TFF: This was the first Trek film that abandoned any pretense of trying to appeal to non-Trekkie viewers. The overlong sequence around the campfire was fun for longtime Trek fans, but it came off as filmed fanfic. The sudden appearance of Sybok, a hitherto never known brother, was more

-inducing than anything else, though I do wonder how it would have played with Sean Connery in the role as originally planned. I frankly find the film unwatchable (how many decks are on the Enterprise, again?) and so it's my big disappointment of the film series - TNG films included.
TUC: Thank god they made TUC. I'd have hated for TFF to have been the finale (which at the time was reported to possibly have been the case). TUC was a timely story, returning to some of the darkness of the first three films, and it revealed layers to the characters that we'd rarely seen. It's certainly the best-written of the TOS films, and pairing old Stratford Festival colleagues Shatner and Christopher Plummer was genius. My only gripe with TUC is that Roddenberry vetoed the plan for Valeris to be Saavik. That would have been incredible and I hope someday someone will create a "fan edit" that changes the character's name so we can see how the story was originally intended to unfold...
As for the TNG films, the only one I really liked was First Contact, for much the same reasons I liked TUC. Problem was Undiscovered Country was the last Trek film made with mainstream audiences in mind. The TNG films pretty much required intimate knowledge of TNG, DS9, etc. I did enjoy Nemesis, but it came out at a time when the franchise was collapsing, so I don't even think another Wrath of Khan would have been fondly remembered from that dark era.
Alex