I watched it last last night for the first time in a couple of years. It's of it's time no doubt, and there's some bits that grate now as a result - René Auberjonois whipping out the paper flip chart in particular looks pretty ludicrous today when we all have smartphones and tablets hundreds of years before this film is set, and some of the humour is a bit off - Klingon translating scene I'm looking at you. I defy anyone not to laugh at that look that Bones gives when Martia starts kissing Kirk and the resulting 'what is it with you anyway' line - pure McCoy gold.
Some of the racism is a little off too, but it doesn't bother me as much as some folk, I'm happy with Kirk's position in this - Klingons have been a big adversary of his all his career, they murdered his estranged son that he had only just got back, which also resulted in the destruction of the Enterprise - that gets a pass for me, but some of the other bits stood out to me - 'they all look alike' and 'did you see the way they ate' etc but I can see why this was woven into the narrative as it's kind of the whole point of the film that humans have to face any prejudice they have against the Klingons in order to accept them. It's heavy handed but doesn't drag the film down too much.
I still think the majority of the visuals hold up pretty well, especially after the disaster of the previous movie, and I loved seeing the TMP Klingon battlecruiser again - It's a shame that ship wasn't involved in the final battle, which I found to be a little lacking compared to the battles in TWOK, but was still pretty decent.
Overall it's not the best Trek movie - I put it around 5th or 6th place but it's still a damn entertaining and satisfying film.