As previously reported, pre-ordering Batman: Arkham Knight from GameStop allows one to avail the Red Hood Story Pack DLC, where you get to play as the Red Hood. This morning, GameStop showed off gameplay footage from this DLC.
In addition to the Red Hood DLC, the Harley Quinn DLC pack is also available as a pre-order bonus for Batman: Arkham Knight. You can catch a glimpse of that here.
Batman: Arkham Knight will be available on June 23rd.