First, Peter Jackson took Tolkien's middle-aged witty gentleman Frodo Baggins and turned him into a boy with the eyes of a raped rabbit. (I am not even going to mention the whole Frodo–Sam relationship on-screen.)
This is how Frodo was supposed to look:
Now Peter Jackson is going to abuse the Hobbit.
Tell me, when you read the book, did you think the dwarves looked like this (full image)?
Now, these are some good actors. James Nesbitt (Murphy's Law, Jekyll), fourth from the left, is actually properly cast. But Richard Armitage (probably known to the most from Robin Hood), in the center, cast as Thorin Oakenshield, makes the King Under the Mountain look like a playboy.
And Aidan Turner (from Being Human), first on the right, looks actually more elven than dwarven. In fact, perhaps he should've been Legolas. Or one of the forest elves from the Hobbit. (And what is he holding in his hands? Is that a sword or a bludgeon?)
According to my wife, the dwarves are supposed to look more like this:
This is my cast of Balin, my favorite of Thorin's dwarves (although Rabbi Kaplan is actually very tall, so casting him as a dwarf would be difficult):
And my cast of Thorin (not necessarily due to the looks, but due to the character):