Nice work with the lighting in this picture, I love how your use of both cold and warm light sources on his different sides creates an atmosphere that suggests the man is in a warm room (maybe with a fire?), but a room that possibly has a large window to a cold and dark winters day. The light really works to create a setting as well as making the contours or his face more dramatic.
I love what you've done with the warm and cold highlights, they give wonderful depth and life. Your brushwork too is nicely sparing, hap hazard yet with that just right feel to it and looking confident. Very nice portrait.