Call of Duty 4: Part of me gets nuked, part of me gets to save the world from evil Russians/Azerbaijanis/whatever. Plus I get a sweet mohawk, and my voice is done by Kevin McKidd. Solid.
Fallout New Vegas: Sneaky sniper with a bunch of awesome badass friends, a suite and backpack full of fun weapons and explosives and a sexy huntress chick who I can visit and have sex with at my leisure, AND I get to decide the outcome of an entire war and the fate of an entire region of the world. Nice.
Metro 2033: Uhhhhhhhhhh...just keep the librarians and demons away from me, please. ANYTHING BUT THE LIBRARIANS AND DEMONS! :'( (On Hard, mind you, they're pushovers on easy and normal)