I think it would be fun to discuss everybody's favorite shooter engine. Mine would have to be the Unreal Engine because the gunfights always seem to be most visceral of the shooters I play, and it makes for some really nice imagery. I don't know why this is, but when I played Star Wars: Republic Commando, Gears of War 2, and Bioshock, I just got a feeling of the gunfights being well-coordinated and the controls being responsive.