it's a nice render, simple design. I'm just going to pick at some technical issues:
There are a couple spots which I'm not quite convinced by. The first is the right arm. With his hand pointed so much in our direction, his sleeve ought to have a slightly more rounded opening, and the arm/shoulder itself looks a tad on the small side. I'd also bend up his collar on that side to react to the reaching. That pinky may just be a little bit too outwardly bent for the angle of the hand.
The other thing is his left hand. The fingers are too small for the size of the hand. I'd also shorten that forearm just a touch.
Giving his sleeves a little bit more wrinkles would make the clothing more believable.
How, nicely colored, well done on the hands and cool subject.
I agree with Dave on the sleeve on his right arm, it should be a bit wider. I love the way you did those hands, although I must also agree about the pinky, it's hard to get the first bone of your pinky that much to the side. Try it... Finally his left forearm is too long.
The lighting seems to be inconsistent. Where does it come from? Top left for face, mid right for his right hand and left for his left hand and the holes in his chest? I'd like to see its direction/location confirmed by some cast shadows or some more shading on his body maybe?
Love to see the finished piece