You have to wonder how realistic they could make a mythological world seem but I know and respect Kenneth Branagh's great work with characters, and I have to hand it to them, Asgard and its characters come out well including the shifting between the worlds. They manage to explain their existence/relationship to earth in a believable way. As for the movie as a whole, I loved it. Excellent choices in casting Thor and Odin especially. The hero's shift to humility/servant-like attitude, the relationship and respect or lack thereof between father and sons, and the theme of self-sacrifice give the story the depth that it needs. Colorful, rich visuals and nice dialogue.
I thought this was an interesting quote from IMDB.com: "Kenneth Branagh conceptualized this film as a Norse/comic-book twist on William Shakespeare's Henry V, which was about a young king who underwent trials and tribulations: fighting a war, courting a girl from another land, trying to live up to the example set by his father (a beloved king), and basic character development."