As stated above, the arms are too long even for Sonic, however, one of the major flaws is with his anatomy. Anybody standing like that and they'd fall down quickly, next time, build a wireframe skeleton of the character (In a pose, try being in the pose yourself before spriting it). The running is also very exaggerated, nobody in their right mind would run like that unless it's for comedical purposes in an anime. Also, why the green shade for Super Sonic? Why?
His head seems to turn slightly to face us, and a bit sideways, but his body is somewhat similar but still different. You'll need to revise this a lot, I'm sorry. Also, the majority of the poses wouldn't work right if you dared try it yourself, the way it looks, it seems a bit impossible.
EDIT: Also, his fists are HUGE! 0.o;