Gotham City Imposters was a pretty good multiplayer first-person shooter made by monolith productions that was abandoned before it could hit its stride. The extensive customization is the best part of it, clowns on rollerskates with swords and sniper rifles fighting against batmen with assault rifles and bottle rocket launchers all with custom skins applied to look like pizza or pink cheetah camo. who's up for a few rounds? It is free after all.