I really like how you have left it unfinished. Makes you focus more on the detail work you did to the eyes and the glasses. Only thing I would suggest to make this drawing better is on his right ear (left side of page) would be to add more detail under the arm of the glasses, where his hair is. That one spot is distracting. To have all that detail there and then a bland gray area looks out of place.
I do really like the picture over all. Good work. And keep it.