I'm not much of an artist, so don't mind me, but I THINK what might be missing is a consistent light source. In the Despain Pixel Academy subforum, under the contests etc forum, you'll see a link to a... here,
Derek Yu's tutorial.
The upper crotch area, for example, seems unnaturally bright. In some areas there's possibly not enough contrast for the colors to really be distinguished in the small view - the legs, for example. I'd have a slightly darker line of pixels on the skin under the hair, for more of a transition on the forehead. I think this might be taken care of better though if you experiment with the lighting part of the tutorial.
Bear in mind I'm no artist though, so don't take anything I say as fact or too personally, just as something that might be worth considering checking out