great
the contrast is wonderful and everything is very easy to see yet well balanced. now try improving your pixel clusters. how i do it is i sorta chicken scratch in an idea of the cluster i want. after i can see that the cluster will work, i go back and refine, noting every pixel's influence on the cluster. this may mean altering several pixels or maybe only 1-3. sometimes i have to AA a particularly complicated cluster into the right shape.
many of your pixel clusters can be refined into a more controlled shape, but particularly ugly clusters are the light hair clusters sticking out of the hair in shadow-the clusters near the bottom right of her hair. the more refined your clusters, the better your pixel art will be.
take another crack at the eyes. something like that just may take practice and trial and error and lots of moving of single pixels.
lastly, it might not be necessary to shade the head. we already get the round feel of the head by the shape and shading of the hair on top of her head. shading the head may take away from the anime feel in this case, making it look more like a toy doll, but i could be wrong