Pretty close to being the worst of the Marvel movies, but... how can you skip one that introduces so many major elements of the larger cinematic universe?
Weak points: pretty much everything involving the human characters, the underdeveloped relationship with Natalie Portman's Jane Foster, and the excessive liberties taken with Norse mythology (sorry, I'm a purist).
Strengths: Tom Hiddleston and Chris Hemsworth. They're perfectly cast, and they play off each other well.
Overall, it's a pretty lightweight affair, but fans of the other Marvel movies should definitely watch it -- if only for the sake of getting more out of subsequent films involving these characters. Plus, "Thor 2" is a major improvement.