You should try and get the balls of his feet boucning. Rather than make him sort of contract, have his body bounce up and down to the left and right, with his toes locked in place. But this may be a bit too drastic...
I think his hip movement from left to right is a bit weird. I think his cape exaggerates it; reduce the movement on that.
Also, his right arm is moving a bit awkardly. I think if you made it about 2 times slower, (the arm seperately or the whole animation) it would look more natural. (Maybe make his hand move in a circle, too.)
Another thing, I think rather than contracting his knees quickly, he should fluidly bend and extend them, with equal frames for both.