Actually, Takei was fine until TUC, when he took the captain's role as a reason to "go boldly." Walter Koenig was actually better in the movies than in the TV series - but then again, he was always the least crabby of the group. Maybe because he was added later, or his own documented low sense of self-worth. He objected to Shatner taking control on the set, but never said the show was an ensemble or that Chekov should have been an Admiral or something. Jimmy Doohan was fine until Generations, which was when he phoned it in. I dunno, I think they did okay for the most part. As much as I don't think Takei should headline the Star Trek Universe, I still consider them all important parts of TOS as a whole and it was cool to have them all reunite.
Not that I would have MISSED Sulu if he bailed, but all the same, I'm glad they were all there.