I love the pose. He looks so comfy & natural, and the fact that you can see his thumb is great!
Exposure, focus, and DOF could all be improved. It looks like the sharpest area of the image is around his elbow. What AF mode were you using and where were you targeting? Are you using available light only, or is flash an option? If you can bounce flash off of the ceiling, or a nearby wall, I'd say close up the aperture a stop or two and add some light.