The Next Generation movies in the Star Trek series, generally speaking, stink. Which is unfortunate, since in some ways the TNG series was better than the original Trek. However, the movies generally vary from pure cheese to holier-than-thou piffle.
First Contact is a good, fun movie overall, with pretty good effects shots and plenty of generally well-executed action. However, it also has some defects that can really get on your nerves.
-The plot is dumb. Time travel has been done to death in Trek, and is a real groaner when you realize that it is being done yet again.
-The movie beats into the ground the Star Trek plot gimmick of "we've found a mysterious energy field, let's duplicate it/follow it/etc." We've gone from the first Star Trek movie (crappy in other ways), which at least gave a nod to real science, to the end of TNG, where they just make up fake scientific-sounding B.S. AT WILL as a plot fix.
-Picard acting like Ahab from "Moby Dick" is way overdone, the worst acting by Stewart EVER. Pure scene-chewing cheese, and the PC bit of having the skinny black chick talk reason into him is just dumb and annoying, since she was a throw-away moron of a character. If you are going to be PC for no reason, at least have Geordi do it, we've established that LeVar Burton's character has a brain, and he can actually ACT, unlike what's-her-face.
-Making the Cochrane character such a total jerk was a BIG mistake. Yes, it was intentional, but it was a bad decision... it makes you hope he gets shot in the head instead of fulfill history, and makes the whole middle section of the movie drag.
Overall, however, it is a fun movie and the only TNG movie worth watching.