In many ways the choice for the head of the party of dwarves was always going to be the most difficult: faced not only with the issues of the character himself, the film-makers were also faced with some issues hanging over from the success of the LOTR trilogy.
Unfortunately, the casting of TV actor Richard Armitage was not the smartest move.
As Thorin, Armitage needed to show regality as well as pig-headedness that Tolkien wrote into all of his dwarf characters, but he was clearly also told to take a significant lead from Viggo Mortensen's Aragorn, albeit played slightly more grumpily, and the effect was reductive. The comparison between the two, drawn by the similar ways the characters were brought to screen emphasised that Armitage is the lesser actor. Yes, his character is presented in such a way that we know he's supposed to be much more important than everyone else, but like The Hobbit itself, by tonal proximity to the Lord Of The Rings, his performance is simply shown up as a little too light-weight.