What's the best game?

I haven't bought a game for like 2 months now so I need some advice on what game to get...

What's the best game out for the 360 so far that has the best story mode, takes long to complete and is fun.

what games do you have? my top three are oblivion, gears, and gta: sa

suggestions for longlasting games: oblivion, viva pinata, marvel ultimate alliance, dead rising

suggestions for insanely fun games: gears of war, gta games from xbox, kotor, ninja gaiden

You just descibed Oblivion, but if you have a friend to play with, I would suggest Gears for its insane coop.