The eyes look too close together, with too prominent lashes (which make the eyes look female). There is no consistecy in the lighting, and the skin tones are all over the place. There are various anatomical issues related to the shape of the head and the arrangement of the features. The hair is presently rather unconvincing, especially at the forehead line. The mouth and ear also have many faults.
Not bad, however, It has some major flaws- mostly anatomical.
The figure's eyes are too close to one another, even for that profile. The eyes themselves look too large for the skull. The skull itself is too vertical and wonky. The nose is lopesided, the ear too large and the chin's mistakes was covered by the makeshift beard.
Google some images of a human skull or face and do some personal studies.
Still trying to think of a clever saying.
Homocide and Apple Liquid: A Sketchbook
I think if you flipped this you may see how wonky the face is. The rendering should wait until the basic proportions and angles are right. For what it's worth, I like the rendering so far. It's a shame so much of it will have to be redone.
'Cuz life is full of your regrets, and I should be one...
Dark skin tones are a pain in any medium. Aside from fine points in anatomy (which I am criticized for a lot) I'd take some time to study how light falls on on faces and the general structure of the face. Byrne Hogarth wrote an excelent book call "Dynamic light and Shadow"
I'm by no means a master of this, but I hope the book will help.