Very interesting discussion. My thoughts are similar to Eddie's, except I've read quite a few Thor comics and am a huge fan of the characters (Conan, Thor and Punisher are the only ongoing comics I get these days). That doesn't make me an authority, I'm just pointing out that I had a lot of expectations going in.
I enjoyed the movie alot, but when it ends there's definitely a sense of 'wait, is that it?' It feels truncated, like we're watching an action-focused cut rather than a complete story. It feels like we go from arrogant Thor to making breakfast Thor too quickly.
What the film needs is for Thor to want to change himself to make Jane want him. As it stands, his arrogant and cocky nature are almost attractive to Jane, so he doesn't have to change to get the girl. Thor never has that 'this woman I like doesn't like me, why?' moment of self-reflection. He never truly realises that he's arrogant. His transformation is only that he becomes self-less. That to me is only half the arc. Thor isn't worthy to be king because of a number of character flaws, but the story doesn't tackle them all.
What the film also needs is to get rid of the pseudo-LOTR opening and the presentation of the frost giants as one-dimensional orc-like beings intent on wanton destruction. They need to have a valid story of their own. The war with the Asgardians needs to be more about a pre-determined fate than about good vs evil. With the relevation that their King does know about the infiltration mission at the start, any hint of them being a race with their own problems is thrown out the window. As a result, Odin's reluctance for war seems odd, and the audience is left questioning why Thor shouldn't go off and bust heads. They don't see why Thor was wrong. If you can't really agree that a character is flawed, it somewhat undermines the ensuing transformation. And as others have said, Thor's turnaround to not wanting that race destroyed is made puzzling because at no point have we had any hint that the frost giants are redeemable. Thor hasn't had a revelation that they aren't the boogeymen he's grown up wanting to fight. There's a definite disconnect there, as if his experience with humans should have informed him of the worth of other races. Considering there was a line in a trailer where he says something like 'oh no, this is earth isn't it', I suspect that there are some deleted scenes that perhaps could make this whole thing make more dramatic sense.
All the problems I feel come from the story though - the acting, directing, art design and action were all great. Some of the Odin-Thor-Loki stuff especially was great. The whole Loki character and his story was probably its strongest point. It took unexpected turns and for me was geniunely moving and sympathetic.
There's a masterpiece in there somewhere. I really hope that there's a director's cut coming.