A very nice study because of the great facial expression. The dark background works great and the intensity could have been lifted higher by a shift in the gama adjustment. However, the composition is good and this alone deserves a bump.
i don't know anything about portraiture, so i'm using your image as a guinnea pig as to what i think i would or wouldn't do in this situation, as well as what i notice and get out of your image.
my initial reaction is it is a bit too centered. i like the lighting, the expression, the pose. i especially like the range of colors across your face--very nice work. it just feels that there is a bit too much space behind your head (maybe take a look at a 1.25:1 crop from the left?). all the same, great work, and good luck!