Pretty cool, all the proportions and details are your own decision, but I'll post a few suggestions anyway.
I'd make the eyes slightly larger (compared to the huge eye sockets) and more spherical. I would also make the head a little less flat. You have quite alot of geometry in the base-mesh (the low poly one), it is wise to only insert new edges and detail when you need it to prevent the model from becoming increasingly heavy as SubD or Poly Smooth (2 iterations). It is not bad at all for a model without reference pics. Keep it up and get your friend to do one too.