I think people have touched on this, but there's something about it that makes it look like bas relief work instead of a three-dimensional form.

I felt that it would be hard to continue without seeing this piece against a more full reduction to form and value. Here it's slightly overplayed and not hugely scientific, bringing up the central cheekbone to play on the light. The line I like to use what talking about formal work is "start by making strong value judgments", the meaning of which is twofold:
- Make observed or at very least informed delineations of shapes based not on the information you're trying to convey, but on the brightest and darkest shapes (strong values) and place them.
- Make a clear decision about where you're going to draw attention (I chose the depth of the eyes as my focus, but it could as easily be anywhere else) and mark these with much greater focus and contrast.
I suggest studying some statuary or black-and-white photography, purely for the reason that it removes a lot of the confusing color and, in the case of statues, the values and colors of the material itself (leaving only form).
On a less technical note -
the Heidelberg-type scar he's sporting, where did he get it (that is, what kind of weapon would strike at such an odd angle?), how is it so deep and yet missed his eye completely, and most importantly what on earth does it add to the character?
What are we suppoed to get from his expression? He looks a bit dazed, but little else. I realize portraits should be somewhat generic if paired with endless dialogue boxes, but there should still be something conveyed, no?