The trick is, what I feel is missing, is volume and structure. The rendering is there, but the volumes are not . Did you draw this from a photograph? The ears are a bit off, so does the mouth and the eyes (The quasimodo effect) I did a redline, and I found that the proportions are a bit on the wack side too.
No probs though, just practise the planes of the head a bit and not to mention proportions, you are good to go :)