Just watched the video myself and I'm not particularly impressed either. The graphics and gameplay do look fantastic, but not much of a jump over Halo 2, which is surprising considering how absurdly great Halo 2 looked compared to Halo when they first showed it off and the fact its a on a new(er) console.
Of course, the finished product may end up looking better, but once you get into beta testing, wouldn't that signify that most of the major code is already pinned down?