The light and dark values are pretty good. I agree the neck is pretty thin. If it were not for the light outline around the muzzle and nose, It would be hard to see the form of the muzzle. Right now the forehead appears to be flat. The ears, eye sockets and muzzle often affect the geometry of the head.
I made a rough drawover . My teacher always told me that if the drawing aren't good , everything else doesn't care. I am not professional but at least I can guide you a little bit . Cheers and good luck , keep going !