i honestly feel it could be between gears of war and oblivion. both games feature the 360 at its best. have excellent gameplay and awesome replayability factor.
-SinisterMinistr- im not gonna say you're wrong b/c really, you're not. after beating the game on insane, there really in nothing more to accomplish other than killing people online...which is infinitly fun.
oblivion is just too damned huge of a game and developers are constantly adding shit to marketplace for us to download to make the game upwards of at least 20 hours longer (knights of nine is roughly 10 hours in itself!), adding to its already 30+ hours of gameplay! fuck that, but i love the game! so when it comes down to it, its honestly a balls out brawl between those 2 heavy hitters.