Rocksteady have confirmed that this will be the final entry in the Arkham series. The game is set one year after the events of Arkham City with Batman at the peak of his powers, but set to face off against all his foes who are teaming up, including Scarecrow, Penguin, Two-Face and Harley Quinn. The game will be set in a bigger Arkham City with wider, drivable streets.
So it sounds like it is moving even more towards an open world type game. It also sounds very 60s Batman with all the villains teaming up together.