One of the problems is that the right leg, the chars. left leg is streching too much. You don't stretch your leg that much when you are walking if this was a runninganimation that would have worked fine. Also I think the animation needs a coupple of more frames. The right leg from the sprites view is good, but not the left. the foot seems to get the wrong angle when it goes forward and it is waaay too long. It should be just the same frames from the other leg but on the other side and reverse. Also I think it is much to lent backward as Tsukasa said.
But most important, 2 more frames on each round and short down the left leg!