You've got some good contrast in there, and the fingers and thumb are good as well. Some nice details with the creases, but the lines are a little thick. They are meant to be dark, but try to keep it dark and thin. The shape of the hand is off too and it feels kind of flat and that's because overall it's too gray. Instead of having a gray tone, which is what you think may be the correct shading for it, try to push the light and dark part of the hands even further so that you arrive at the mean through extremes. (Thank you sarge for expanding my vocabulary with that phrase, although credit goes to me for it's application here.) Also, you may want to add something to the background.