I don't like the way the arm just...curves out of the torso without a shoulder.
Expanding on what Crab said, I don't necessarily think you should make this in vector, but rather, that you should take advantage of the benefits of pixeling it, such as nice, crisp detail. Like on your hair there, you can keep it simple, but I think some hilights would do the piece some good. And when you get to the face, it should be as detailed as possible without breaking the style. Like, details unique to pixel art. By which I mean pixel small details. You get meh?