http://www.pcgamer.com/2012/05/03/elder-scrolls-online-announced-an-mmo-set-in-the-world-of-skyrim/
It has been rumored for months (years?) now, but we finally have confirmation.
It will be set 1000 years before the events of Skyrim, where Molag Bal is attempting to swallow up Tamriel into his plane of Oblivion. Looks interesting so far.

I hope it feels like the Elder Scrolls and not something totally different.
Indeed, that worried me too. I have been resistant to the idea of an Elder Scrolls MMO since the rumors started but I will play it regardless, because Bethesda.
http://www.youtube.com/watch?feature=player_embedded&v=I6m9-Dret0U
Screenshot dropped:
http://www.gameinformer.com/games/the_elder_scrolls_online/b/pc/archive/2012/05/04/first-screen-and-details-surrounding-elders-scrolls-online.aspx