I think the picture looks great. I did notice though that the right side of his face is in shadow. The left side seems to be in contact with a light source. I also think that maybe some stronger ( light to dark) tones might help overall. I think that looking at your sketch, it would imply that he was in direct sunlight.
lol....ooooo your so right! the funny part is.... I was so focused on trying to catch the likeness that I forgot about everything else...but i've recently being trying to practice shading and focusing on differentiating lights and shadows from one another. you wouldnt happen to know how to shade a stubble beard??.... would you?? lol.