I was surprised by how much I enjoyed Halo when I finally got around to it, and I had high hopes for Halo 2. The sequel brings many improvements: more variety in weapons, enemies and locations, and the ability to dual wield weapons. Playing the game from both the perspective of the Marines and of the Covenant is a nice twist. Yet somehow, it doesn't quite measure up to the first game.
The levels where you play as Master Chief—at least in the beginning—feel more like staged set pieces, some times to the point of breaking the suspension of disbelief. The graphics are improved—particularly the real time cut scenes, but by going with a more realistic color palate, it can be tricky to see what's going on and frankly I missed "the purple" of Halo.
However, the story from the Covenant side is well done, and once the game progresses, Master Chief's story makes up for its lackluster beginning. My cohort Eric pointed out that Halo 2 has the best "alien chatter" of the series. The variety of things the Grunts, Elites and Brutes say is really impressive.
This is still a very good game, and I am glad that I played it. Having played and beaten Halo 3—which takes the best from both Halo and Halo 2, yet takes very few risks—I appreciate the chances the developers took.