Nice, dynamic shapes and bold use of tone but the torso seems unnaturally compressed. Looks like the rib cage is nestling down deep in the pelvis! Facial features detract from the whole- often best just to throw them into shadow and suggest rather than define, as you did with the thumb. Hair is sloppy although the direction is clearly defined-could afford to be more bold with the hair. CONTRAST is the key to exciting imagery! Where you have the rim light on the back meeting the darker background-the contrast could be greater here ie. darker b/g.Highest contrast should be in that knee closest to 'us'.