Looks nice! There are a few things I'd suggest to help this piece stand out more. For instance, maybe make the nose a lighter color, as if the light is hitting off of it. Another thing to keep in mind is to not over use dithering. I used to dither a lot but I found it makes pieces look much cleaner just to use AA and good contrast.
I really love it the only critic I would say is the nose is a little strange otherwise it's really good
Thanks for the suggestions