Excellent Movie, one of my favourites! This has comedy, has action, has moral meaning, and has fun! Shame they don't make movies like this anymore :( I would rate this movie as being my second favourite Star Trek movie (the first being First Contact). It is quite different from more recent movies like Star Trek (2009), Nemesis etc, which are much darker and violent.
I'd say the plot is the weak point, the acting gets a little silly, but to be honest it's being there with these classic characters that is part of the fun!