There is a ton more work to be done on the face before you start worrying about neck and shoulders.
The human face is an incredibly complex thing with scads of little muscles and details. You need to think more in terms of these little details. Here's a quick edit:

Very quick, and I'm not saying it's perfect (my strong speculars are pretty inappropriate

), but let's go over a few things in no particular order, despite the fact that they're numbered:
1) Proportions. Human's don't generally have noses that short or upper lips that tall. Always consult references of what you're drawing; Google Images search is invaluable for this sort of study. Pick up a facial anatomy book if you want to get serious; these usually have wonderful proportion guidelines.
2) Nose. The human nose alone is an incredibly complex thing! It can't be simplified into a rectangle if you're trying to draw realistically. Think carefully about nostrils, not just the holes, but the way those passages shape the nose as a whole. Think more about how it blends smoothly in with the facial plane rather than being simply plugged in. Think about how it interacts and blends with the brow (something I didn't address in my edit but meant to)
3) Masses and levels of depth. When shading anything, think about breaking it down into basic shapes--primitives--and shade accordingly. This will help you define your masses clearly. Your shading around the chin and brow, for example, is very illogical. And like tocky was saying, use all your colors to the fullest! Use them to define clear levels of depth. When drawing a face, you can almost think of each shade as defining a new plane.
4) Proportions again. Remember that the human head is divided into two roughly equal halves of cranial mass and facial mass, with the the center being the eyes (technically the bottom of the brow). With this in mind, I think his forehead needs to be a tad taller (though, again, I didn't address this in my edit).
5) The little things. The depression under the nose that separates the upper lip into two halves (there's a technical name for it that I can never remember), wrinkles and folds (like those in the edit originating from the nose), cheekbones, jaw line, brow ridge, etc., etc. Again, an anatomy book can be your best friend, but even just looking at photos of faces is a great way to study.