What game do you think has the best soundtrack?

Mega Man X. I listen to that soundtrack almost daily.

The Elder Scroll Oblivion - I like it more than Skyrim's...more epic.

Jet Set Radio Future - I still listen to this amazing soundtrack. It will get you going in the morning.

Persona 3 FES - It just rocks. P4 is good, too but I spent so much time with P3 that its OST was just burned into my brain.

On top of my head I can think of Metal Gear Rising, Asuara's Wrath, Crypt of the Necrodancer, Metal Gear 3 and 4, Warhammer 40K:Dawn of War II, Rayman Legends, Donkey Kong Tropical Freeze.