The fundamental first person shoot em up.
My son played the single player game for a few hours, then moved into the online play. He never did go back to the single player game... I suppose that means something.
Online play was fun. It's a team play thing, and seemed fairly smooth.
Thats about all I have to say about that.... One note though... I didn't like the scrolling movement at all. I'd watch my son play and actually start to get sick to my stomach after a while. I attribute it to the movement in the game. Or the Asiago I was having with my Fat Tire was bad... but who can tell with Asiago?