What a cutie! I don't think his head is too wide! I love big heads.
I'm guessing by his name that he's a Paint, correct? How old is he?
At first glance, I thought he was a little downhill too. But then, look at the white beam (on ceiling) above him...it's also "downhill." I think the camera angle is just a little off. If you were to rotate the whole photo 1 degree counter-clockwise, I'm sure Painter would look level/balanced.
I really like him a lot...maybe work on that tail though, it's a little scraggly.