Left me wanting more.
Oh don't get me wrong, the game is great. Pretty graphics, awesome gameplay, same ol' multi-player (which I like), good story...BUT when my friend and I beat the game and we saw what would be the ending cut-scene, we looked at each other puzzled and the first words out of our mouths was "That's it?!"
My problem is that it was VERY obvious that they were holding out for the sequel. Not that that's a problem, but the first Halo at least ended that portion of the story and tied up all the loose ends, I personally would have liked to see that in this edition. Don't get me wrong, once Halo 3 comes out I'm going to get it, but the cool thing about Halo was that you wanted to play Halo 2 for its innovations, not necessarily for the story, not that the story isn't important either.
Bottom-line is Halo 2 is a really great game. However, I felt kinda cheated by its ending, I would have rather had some ends tied up. It might just be me, but it would have been cool if each game continued the story, but didn't leave any questions at its ending.