Batman will supposedly begin the game with every gadget he had by the end of Arkham Asylum, meaning no strained pretext ("Oops, I lost my utility belt!" or something?) to force players to reacquire it all -- and on top of that, he'll also get smoke bombs, too. Batman will also be able to counter two attacks at once during combat, and will have to solve "more puzzles." There will also be the addition of "side-missions;" various gangs roaming Arkham City that Batman will record in a criminal database; and the Riddler challenges will return, but Batman now needs to find people who work for the Riddler to initiate them.
Rocksteady is becoming my favourite studio. I hate when they make you forget and lose everything.