*contains big spoilers*
Just beat it this morning. My problem is that the game seemed so much shorter than Halo 2, which was this huge, sweeping, epic adventure. This was more like a follow-up. I dunno. I guess part of it was that the only two locales in the whole game are New Mombasa and the Ark, unlike Halo 2 where you had the MAC gun station, New Mombasa, the hanging cable station on Alpha Halo, several different climate zones on Delta Halo, the whole journey to the Library and fighting your way through the civil war on High Charity.
The (pre-credits)ending too was very underwhelming. Not only did we not get to see a big, drawn out sequence of the Gravemind being incinerated and screaming as his plans go to ruin, which should've been the entire focus of the ending as it was basically the whole point of the game, but we didn't even get to see the new(Omega?) Halo detonate or the portal itself close. We have to learn about it after the fact in dialogue? Blah. The post-credits ending sort of saved the whole thing.
Also, it sucked to see the Arbiter's role so downplayed so much. I loved his story in the last game, and he's pretty much the series best, most developed character.
Still, the gameplay, graphics and new equipment system made up for almost every flaw. I'd give this a 9.25/10, as opposed to Halo 2's perfect 10 in every field.