The original "Halo" was one of the most widely praised and popular first person shooters out there, and any sequel would surely have its work cut out for it. But it looks like, on most fronts, "Halo 2" fails to disappoint. OK, some of the elements of the story leave a little to be desired and of course there are shortcomings here and there, but generally the consensus seems be that it is a fine game, and a great sequel to the original. Alright, the single player portions are a little lacking but there seems to be just so much content in "Halo 2" and so much action that its just a great game, end of story. Go here
for a great review of this game.