Easily the most dithering I've ever used.
Dithering in faces is anathema
There are very few cases where it works, as in
Mandrill's entry, but most of the time it just doesn't. Faces are what our brains have evolved to extract the most detail from, they are also usually the focus of a piece. You just want everything to be pixel-crisp.
Also this ref is not very useful, you can't see any detail in there, it has even less resolution than your pixel piece.
You should sketch your features in the mirror and use that as a complementary ref =)