This guy is amazing! His facial hair doesn't get blended in with the shading which is great! You can really see the light in both his eyes and the face shape is realistic! You have made it so he looks his age and not younger with the shading under his eyes!
My suggestions are the hair first. I'm not sure if this is personal opinion but it doesn't seem to go with him, it seems it doesn't fit his character. And secondly, the shading. I think you have too many light points and are in need of some darker tones on quite a bit of his face, especially his nose as usually they have a fine bit of shading.
But this is amazingly done and I am definitely putting it in my favorites!