The next game in Rocksteady Studios' (Batman: Arkham City/Batman: Arkham Asylum) Batman series will be a "highly stylized" prequel. The game will reportedly detail Batman's first encounter with the Joker, and is based on the Silver Age of DC comics from the 1950s. We discussed this in length in our latest episode of KJBcast, I Might Be Dead By Then!
The new Batman game is not likely to arrive until 2014 at the earliest. Additionally, Mark Hamill said last October that he will not reprise his role as the Joker in the next game. So all of this is still quite up in the air, however, the game IS happening.