It's a really wonderful drawing, and I think it would have turned out excellent if you had pushed some of the shadow more. Like some areas, especially behind the ear, could have been darker. Right now your value level seems to only be around 10-40%, which isn't much if you think about. Try to push the value to the 70-80%. It'll really make your drawings pop. I had this problem for the longest time, and the best thing I can tell, as my mentor told me, you is to not be afraid of pushing your values and messing up. If you mess up, hey, at least you know how to fix it the next time, right?
I really love your clean lines though, and your attention to the details, like the little crinkles in the skin. I think, aside from the value, it's a really wonderful drawing. You should be very proud of it.