The shading is a little heavy because you have visible lines of where the shadow begins and ends. For example if you take this picture, then take your finger and rub the shadows with your fingertip, you'll see how the smear and blend. if you look at anything that has shadowing effects on it, there is no solid line, it feathers and blends. =] (Simply answering for the previous statement aswell as I do have to admit I agree)
I personally enjoy this drawing though, granted the shading could be a lot better but as far as "scetch pad" goes, I like it, her face is the best part in my opinion. Practice makes perfect, the more you draw the better you will get and by no means is this drawing bad at all =] I give you 4 stars because of the effort and skill you do have, and I keep the 5th star to motivate you :P
