You seem to have a very ambiguous light source. Shade the pixel art so that it looks like the light is coming from one direction. Right now you just seem to be shading around the edges of the pixel art.
I see you've attempted at least some anti-aliasing, which is good. It needs some around the entire body as well though.
The outline struggles in some places, sometimes not being smooth enough(head... squiggly... thing o-o; ), and in others not being a one pixel thick line (around the arms and chest)