After much speculation it has been confirmed that Mads Mikkelsen will be the main villain in Thor 2, but his role has not been unveiled yet. Here is the source.
Mads Mikkelsen is a great actor, Valhalla Rising was epic. He has the acting potential to be one of the best Marvel villains to date, right up there with Tom Hiddleston. Wishful thinking, anyway, Mickey Rourke is also a good actor, and yet he was less than memorable, IMO.
@CaioTrubat: 616 Loki and the Jotuns looked ridiculous on paper too, which is a recurring trait held by almost all things related to Asgard in that universe. The beauty of the new medium is that they can take characters to different places and drastically change their origins, appearance, demeanor, abilities, etc.
@Mercy_: I loved the way he played his character as a Wolverine type: a reluctant but insanely skilled warrior who said little and knew much.