I do not like the placement of the eyes and face within the frame...too far to the right...
You could crop it tighter, some off the left edge, some off the top, and in that way make it a much better,more-balanced composition. His contemplative look, thoughtful hand position,and downward glance are ALL excellent, and well-intgrated. I just think the framing is "off". It is a wonderful "look" at the sitter. Perhaps a slight, and I mean very slight, bit of dodging on the shadowed eye and cheek might draw us in a bit deeper into his gaze?
It does have a retro feeling to it.