Thor comes back from NY (The Avengers) with Loki to pay for his crimes. Just as he does a Dark Elf who wants to possess the power of evil to make the 9 realms go dark which would magnify his power awakens and wants to reclaim the Aether that was lost to him by Thor's grandfather in an epic battle.
The story is very clean, very simple, and Loki gets roped back in very easily. I loved everything about this movie. It doesn't feel as confusing as the first. If you like comic book movies then you will love this. I don't want to give away any more plot than I have. It's not as sharp and snarky as Joss Wheadon's The Avengers, but it is still visually stunning and sharp writing. It literally picks up and explains why there has been a gap between the first Thor and The Avengers. Everything was tied up and explained how things will move forward. The chemistry between Chris & Natalie is INSANE! They are meant to be an onscreen couple.
And just an FYI if you watch the 2D version there is one extra scene in credits, but if you go to the 3D version there are TWO extra scenes in the credits; one after the movie ends and one when the credits are ALL over at the very very very end. 5 out of 5 stars :)