Good points first: Tom Hiddleston made an excellent Loki, particularly in the early part of the film where you can see Loki subtly manipulating the people around him. Chris Hemsworth (from Melbourne, be it noted) portrayed Thor, and probably did as good a job as could be done, given what he had to work with. And the scene with him sitting in the rain next to Mjollnir was good.
But I must have missed the soul searching scene where Thor decided to be purely defensive. When Loki is about to blow up Jotunheim--well, it wasn't that long ago that Thor was just fine with that, and we didn't really see a reason for him to change from "happy Norse berserker" to "wait, bad guys deserve to live too". It would have been nice to see a little moral quandary at that point. "Blow up Jotunheim? Sounds good! But wait, dear old Dad never did that. He'd probably say it's unjust. And Mom would probably say that if you're unjust to your enemies, you're going to be unjust to your allies sooner or later. And, you know, the whole blow them up with the Bifrost Deathstar Cannon thing is kinda cowardly. So, I tell you what, Loki. You want to go down and take on King Laufey and his thugs mano a mano, then I'm good with that. But nuking the whole realm of Jotenheim is a bit too much, and if you keep trying to do it, I'd have to, you know, whack you in the head with a hammer."
Overall, it didn't feel like a complete movie. Yes, it's part of another six or ten or however many movies for Marvel, but it still felt a bit thin as contrasted with Iron Man or Captain America.
On the other hand...it's a comic book. Maybe I shouldn't be expecting too much complexity.