I have to say Metal Gear Solid Rising.
Metal Gear Solid 4 was a brilliant way to end the series. It was a game made for long time fans, just pure fan service. It was brilliant. Metal Gear Solid Rising has no involvement from Kojima, hence it's Konami wanting to make a quick buck and deciding to cater to the whiny gits who kept complaining about MGS4 being PS3 exclusive.
I really am not holding out much hope for Rising. No Metal Gear game without Kojima's involvement has been good. The series should just end with 4 and be left at that, or at the very most, see if Kojima will be involved in remaking the original 2D Metal Gear games (Metal Gear & Metal Gear 2: Solid Snake).
(also I'm not just being some moron PS3 fanboy who's pissy about Rising being multi platform. I could care less if MGS4 got ported to 360, it'd mean more people get to experience a great game in my eyes)