[quote=@Eisenhorn]As for the Legion trailer, what the hell is the Burning Legion doing back, again? 
[/quote]

I guess the Legion is doing what the Legion is always doing; invading planets and trying to take over them :P

Supposedly, according to the lore, there's like 1000s of planets under legion control, and infinitely more demons(who don't really ever die). I imagine that their leadership is much like that of the Orkz in Warhammer; cut off the head, and the second biggest, baddest demon will take his or her place!

It's like an eternal, never-ending war against a relentless enemy driven towards constant expansion.