This game was rumored to be in the works ever since Arkham Origins was first announced, so I'm not that surprised to see it finally confirmed. Also, since Origins really wasn't that good compared to Rocksteady's Arkham titles, it was a given that they'd announce this one as soon as possible so interest doesn't die down.
In any case, this one is made by Rocksteady, so I'm hoping it will have the quality of the first two games, at least. The only thing I'm a bit worried about is that, with the inclusion of the Batmobile, they tone down the grapple/gliding navigation and stealth aspects. Hopefully they won't do that.