.... Legs are a little outta proportion? Unless he's just wearing some sort of baggy pants or something. The way he's bending his left leg (like, the one on the wall) doesn't look... "right." Perhaps the foot could be fully against the wall (as it's probably not easy to stand with only your heel against the wall). 

...That.. might be it. I'm an artist yet I still fumble with giving advice XD sorry