Currently the top of the list is taken by Deus Ex: Human Revolution, which is surprisingly enough actually looking very promising.
Other games I'm prepared to spend countless hours in are Battlefield 3, Mass Effect 3, and Skyrim. Also HD remakes of MGS 2 and 3, fuck yeah.
EDIT: Oh yeah also Hitman: Absolution, but I'll have to wait and see more of the changes they're making to the formula until I decide whether to get it or not.