Surprised there isn't already a thread on this! Or maybe I missed it.
Anyway, I played the game for a couple of hours last night. It's...amazing! The level of polish on this game is phenomenal. It's certainly the best-looking Xbox 360 game out there. In fact it's up there with Uncharted 2 & 3, graphically speaking. At first I was amazed by the lifelike prerendered cutscene at the start, then the actual in-game engine kicked in and I was smiling from ear to ear.
Storywise, this game has more depth than the entire first trilogy had combined. And while I was wary about a musical score by a new composer, I've got to say the music is still very much Halo. It's atmospheric and engaging.
Gameplay-wise, it's the same Halo we all know and love. I fail to see why some publications are criticizing that...I'm enjoying the heck out of it. I haven't tried any multiplayer yet, obviously, but I'm seriously considering forking over the cost of a Gold membership just for this game.
The game simply rocks, and 343 has seriously improved upon what Bungie built.