A new trailer of the Robin DLC for Batman: Arkham City reveals a number of new challenge maps in which you can play as the Boy Wonder himself, Robin. The DLC includes two challenge maps and a slew of gadgets and gizmos for Robin to use.
You'll be unable to play as Robin in the main storyline, however. It's a pity, because the game could certainly use the expansion in the same way Catwoman gets her own missions during the campaign.
As it is, the DLC will only add two new challenge maps—playable by any of the other playable characters—and Robin to the challenge mode. He gets his own set of gear, which is nice, but most players would much rather play through the campaign than spend time in the melee rooms.
Batman: Arkham City is currently available for the PC, Xbox 360 and PlayStation 3.