Hrm, how can you call co-op minor? Co-op play demands that the game be designed a certain way. Serious Sam works well with co-op because it is a mindless, linear action game with virtually no plot. Unreal 2, on the other hand, actually has a plot that involves the player. Ingame cinematics, scripted events, etc, make Unreal 2 a rather difficult game to add co-op to. Personally, I prefer that they focus all their efforts on the singleplayer game. If I want Unreal multiplayer, I can play UT2k3. Unreal 2 is all about a compelling singleplayer experience and nothing more.