Categories.
I've said it before - definitions circumscribe more than liberate.
I play GTA4, I played as Niko Bellic and tried to do things Niko would or wouldn't do. This included -not- running people over for fun, avoiding cops and murdering everyone who threatened my friends.
I play STALKER, believe me, I'm role-playing and pretending I'm someone else. Because if it was me, I'd just leave.
A lot of these games start to be genre-bending, too. Deus Ex, for example. Hitman, even.
And if it's life-and-death, yeah, I want to feel excited, worried, involved. Seems cheap otherwise.
My game selection reads right now as: Mechwarrior Online, Metro 2033, GW 2, Hitman Abso, Btman Arkham City and Homefront. That's the top row of what I'm playing.
So I'm into immersion.