Gotham City Imposters was originally set to arrive this month, but Warner Bros. Interactive Entertainment (WBIE) has pushed the downloadable multiplayer title back, sticking it with a February release instead.
The game was due out next Tuesday, January 10, for XBLA, PSN, and PC, with a fairly low launch price of $15. As the name implies, players step into the shoes of their own, customizable "imposters," taking sides with either Batman or Joker as unofficial lackeys waging a bizarre urban war in the names of their heroes.
At least this gives you more time to try the game out in advance. The main website proudly declares that open beta is about to begin, so hop on that.