I've always been curious by this cause in my opinion it's the best. It has had the most gameplay changes out of any of the Halo's, it's graphics were great for it's time, and actually I think they still kind of holdup today, and story wise it's great. I thought the way they handled the Arbiters story was really cleverly done, and even the Chiefs parts were good in a very straightforward kind of good. It seems however everyone shits on Halo 2, solely for the cliffhanger ending and I think that's a really unfair point to criticize it on, especially for a middle chapter of a trilogy... I mean Half-Life 2's ending was a hell of a cliffhanger too, but no one calls it out for it. Anyway, just like to hear what other people think, and also what your favorite Halo was and why.
P.S. Only Halo! I don't want to hear how much you think KOTOR or Portal is sooooo much better than Halo in general, this thread is about Halo. I happen to love both those games, just not on this thread.