Picked it up a few days ago. About halfway through the campaign, so no spoilers please! The campaign story reminds me a lot of Halo 2, and it also really hammered home that I need to read the Forerunner novels.
Multiplayer is really fun. The new system they had set up took a little to get used to, and I basically don't crouch anymore, but I'm glad to see my Swat skills have carried over from Halo: Reach!
12/16 - Pallbearer
12/18 - Orange Goblin