As for the story, not many details were revealed, but we know that it takes place in a heavily armed Arkham City, where your favorite Batman villains and thugs are running rampant. Arkham City is apparently a walled-off portion of Gotham City itself, and we can expect a new cast of classic characters and villains as well as new and enhanced gameplay features.
So far, confirmed villains for the game include Mr. Freeze, Catwoman, and that ultimate Batman baddy, The Joker.
The only negative in this story is the wait time. As a huge fan of Arkham Asylum, I don't know if I'll be able to handle waiting around for more than a year, but I guess quality takes time, and the long lead-time indicates that this game is likely to be the antithesis of shovelware.