Yeah, as funny as it sometimes was to see Thor fat, when Prof Hulk was trying to talk to him, saying how Thor saved him and he's going to help Thor now, I don't think Thor was there solely for comic relief. His whole breakdown with Rocket in Asgard while funny because it's not the Thor we're used to, it's also so heartbreaking because he lost everything, even himself. I'm glad he's going with the Guardians who have no expectation of what he should be and how he should be. And I'm glad he saw his mother and not his father. He needed that validation that it's ok to be lost and it's ok to be who you are and not what is expected of you. What's the expression, it' so bad that if you didn't laugh you'd cry. That, for me, is Thor in this movie.
But I laughed a lot at some of the Thor stuff. Chris Hemsworth walked the line between pathos and humor so well. He is perfect as Thor. Actually I can't think of one misstep in casting.