Thought I'd keep ya waiting while I ate my dinner
Its nice man, you have a good sense of placement and proportion, and it looks like you know form pretty well. However your definition of form shows you're a bit to concerned about shape rather than light, and that's the only set back you have, we see light, not lines, so it's much more useful in defining form. Line can define it well when it is suggested, line weight plays a heavy part of this too, I see you trying this on the nose, but ignoring it on the lips. Contrast is what justifies a line and its weight, the difference in colour is not enough in terms of tone to have a line going around the lips, the parts that are made darker by shadow are what you should be suggesting and you'll find the shape of the lips will form on its own. You also seem to be concerned too much with details like hair, its a bad idea to render every single hair, think of the angle of the planes of the hair in relation to the light-source and see if it could be suggested through suggestive shading rather than defining what is actually there.
<3 more please