I don't really do long gaming session, I tend to get bored of a game even if it is totally awesome.
I'm actually ashamed to admit it, but I think it might actually be Homefront, not I might stress because of it being good, but I sat down and decided "Right, if i'm gonna put up with this shit, i'm gonna do it all in one sitting and i did. Luckily for me the single-player campaign was so short, otherwise I might not have made it.
Thinking back, It might actually be when I completed Call of Duty 4 : Modern Warfare's campaign in one sitting. Yeah, I'm going with that. Reflects a hell of a lot better on my gaming cred than Homefront.