Thought we had a thread on this. http://youtu.be/orfMJJEd0wk Does not look that great, but teaming up with Loki will be a good angle.
Yeah, not much of a reveal in that trailer, but I agree that needing Loki's help is interesting, and the villain could be pretty good as well...Christopher Eccleston as Malekith the Accursed. Apparently Loki and Malekith once teamed up together in the comic book version of Thor, but who knows if that will be part of the backstory for the film.
I thought the first Thor was reasonable. Not a terrible film. I really like Loki as a character, he's arrogant, so sure of himself, so... English. I wasn't particularly interested in this film until I saw him in the trailer.