Well having played about 15 hours of halo 3, I'm ready to post some initial impressions.

single player: I'm only on mission 7 of the single player, but it is the best mission so far. the missions are far better than halo or halo 2 as there's so many more open areas and many more vehicle sections. one thing that did disappoint me is some of the new convenant vehicles. the prowler and the chopper are very similar and are basically ghosts or wraiths. anyway apart from that i love the campaign so far and will finish it off by next weekend (playing on heroic by the way)

multiplayer: i have to say this is the best part of the game and i see myself spending a lot of time on it. there are so many options and game modes. i love the match making system, as its very versatile and easy to use and get it to do what you want. the theatre is great as is forge.

overall very good. it has lived up to the hype and i look forward to many years playing it. :D