The face and general proportions look pretty good!
I can't tell if somthing if off about the arm or the twisting of the torso, or if it was just an awkward pose. Maybe a bit of shading around the form to give a bit of information about the seat or couch so I can understand what he is sitting on.
Lots of soft definition in the muscles, some shoulder anatomy would help inform your shading.
Thank You, Kittykatc! The subject was sitting on a cloth covered box of some sort but i see your point. It becomes a difficult viewing for the observer without some point of reference. I'll be more aware of that in the future.