This film is one of the best the Star Trek franchise has produced. It has an exciting plot, epic battles, lighter moments, character scenes... everything you'd expect out of a Star Trek movie.
The premise of the movie is that the Borg travel back in time to assimilate Earth before humanity's first contact and prevent the Federation from forming, while the Enterprise-E follows them to preserve history. From there, the movie follows two distinct plots; the main one on the Enterprise as Picard fights the Borg, and the subplot of getting first contact back on track down on Earth. The Borg plot is, appropriately, the darker, more dramatic of the two, with the Zefram plot providing most of the comic relief. But the Borg plot has its lighter moments, and the Zefram plot has its drama.
The crowning moment of the movie is at the end, when first contact occurs as history records, but with a few extra observers. Mostly dialogue-free, it nevertheless conveys the birth of the Star Trek universe as we know it. It's a powerful scene that exemplifies Star Trek at its best.