Easily the best game of the decade and arguably the best game ever made Arkham Asylum gave fans the chance to run through the corridors of Arkham Asylum in the middle of a riot and kick some crazy villainous ass as Batman, the coolest most in need of anger management comic icon of them all.
Arkham City has a release date of the 21st of October at the moment and will be available on PC, Xbox and PS3. Each version will likely have it's own exclusive content much like the "Play as the Joker" challenge mode on the PS3. Out of the box there are also several versions including a Collectors edition which comes with an exclusive statue similar to the Batman toy which has just been reissued.
Other than a playable map roughly four times the size of Arkham Asylum it comes with a whole load of new classic Batman villains including The Penguin, Riddler, Two Face and a few new playable characters which at the moment include Catwoman and a bad ass looking Robin.
The Catwoman plays a large part in the new story and is playable for roughly 10-20% of the game. She's kind of like Lara Croft meets Selena from Underworld. Pretty kick-ass.
Robin will be a downloadable character who to begin with will only be available if you pre-order the game from certain retailers but will likely be available across the board after 6 months or so.