I love the brushstrokes and the use of contrast around the eyes, nose and mouth. Over all this is a nice study. What I think you could do to keep the form of the head better is to make sure you keep all the lights in the light side, and not put it in the shadow. Also, don't forget that as the light moves down the face, it loses intensity, This is called "light fall off" and helps with form and perspective. I did a paint over but ignore the paint strokes I did, I just wanted to play with the values. I hope this helps, and I look forward to seeing more oil paintings from you :)