I havn't played campaign yet, but I played 2 hours of multiplayer last night. Graphics and sound were amazing and the attention to detail was apparent. I think they did a really good job of borrowing Call of Duty features like the kill cam and loadouts. There's a lot of customization, especially for a Halo game. The aim and firing reminded me more of halo 2 and 3 (which is a good thing). There were a lot of nice little features, like in CTF if the flag was dropped, you could see how much time there was until it goes back to base. Also, your screen had indicators as to where weapons were on the map. The only thing I wasn't thrilled about was the maps seem kind of generic. Then again, I havn't played everyone of them yet, and I havn't played any of the downloadable maps.

Other things I noticed:

-rockets are much weaker
-the human shotgun is beastly and actually has some 1 shot kill range to it.
-ordinance drops are a nice touch.
-vehicles were much weaker, especially banshees.
-spawn points varied much more than I've seen in any Halo.
-similar to COD, you sometimes enter in games already in progress.
-they award you for a lot more than just kills. If you played Reach, you know that it was very hard to get an assist. But in Halo 4, it reverts back to 3 in that regard. Also, you get points for things like distracting, vehicle kills, & vehicle assists.

I havn't played enough to award it best Halo multiplayer yet, but I will say its first impression was on par with my first impression of Halo 2.