Well, he is bigger, but still looks limber enough to mix it up the way Captain America does.
Is it a big role? Sure. "Thor" can be a flop and it won't impact "The Avengers" movie, just like "Hulk", but without a good Cap, there is little chance "Avengers" can work.
If the feet are creeping you out, it is because they are fake. He needed to look barefoot but not risk injury in this photo taken by Amelia Arcus/Splash News