well... if there were any that were in need of a remake, it's that. I don't think I've ever even sat through the whole thing.
Star Trek II was a lot better because they brought in better writers; the screenplay was by a guy who wasn't even familiar with the franchise at first, IIRC.
Gene Roddenberry was good at some things; plot wasn't one of them, I guess.
I'd agree with Mitch that they seemed to go on/off/on/off in terms of quality. I never saw all of III though, so I can't really comment on that. I always thought III was at least decent; not as much of a drop off.
V wasn't very good (Shatner directed it). Given how little time they had (as the cast was getting old) wish they would've used that opportunity to make a really good film about the core characters and races... a war between the Klingons and Romulans or something.