Halo 3.
Can't stop laughing.you should get Call Of Duty Modern Warfare 2.
hahahaha...... hahaha....haha... thats a good one
"by that I mean a game that allows you and a friend to complete the entire campaign in two-player mode, either sitting together or playing together online."
"Call Of Duty Modern Warfare 2" does not fall under that category lol, read more than just his title.
you can play mw2 sitting together on co-op mode...
L4D 1+2, border lands is also ok.

