Arguably the best of all the Star Trek motion pictures. It has some of the best performances of any of the movies, especially those of Shatner (surprising) and Montalban (is that his chest?). Khan just makes such a perfect villain, with his blind hatred and cool catch phrases ("Revenge is a dish best served cold, it is very cold in space"). This movie also had by far the best space battles (with the possible exception of the ST:VI cloaked Bird-of-Prey battle). It seems surprising to me that this was the movie that followed the first one (only ST:V was worse), it having so much more life, creativity, and drama.

There was one glaring continuity problem, however, that only die hard ST fans would catch on to. In the scene where Chekov first finds Khan, Khan mentions that he "never forgets a face" when he is talking to Chekov. Unfortunately for the writers, Walter Koenig had not yet joined the series when the original episode "Space Seed" was shot. Khan was gone long before he ever could have met him.

Other than that it was very well done, and is still, in my opinion, the best of the Star Trek films.