I like this, very original. Try adding multiple opponents in an update, or make multiplayer have multiple people, or teams. Or perhaps multi-teams?(that would be awesome!)
easy as pie, i only ever died because i accidentally went outside once. lacks originality, the balls dont collide with each other, and when a ball hits the wall it aims right for you... 2/5
 "Nano War"){kind=icon}
 "Dungeon Defender"){kind=icon}
 "BlueBall 2"){kind=icon}