I beat Halo 2 the other day... was fairly disappointed with the ending (too open-ended) but surprisingly I discovered a day or two later that the single-player replay value is pretty good. My sister was playing and couldn't pass this one section, so I started playing for her, and I ended up playing it for about 2 hours!
My overall biggest complaint about the game, however, is that it's advertised as an "Invation of Earth - Stop teh Aliens!" kind of game, and only the first third or so of the game is that. I really like the Earth-bound levels more than the Covenant/High Charity levels.
Although kicking Tartarus' ass was great
