to start off, the artwork is fantastic. But to be specific I'm going to give you the pros and cons of this.
Pros: The shading is amazing. Also just the way your drew the main person is amazing. You did the glasses really well, and after looking at the actual picture, I believe you did well on trying to catch the realism.
Cons: Now, with the lines you added around the face, they could used some work, but you didn't need to add them, but thats yp to you. Also with how the hair looks, maybe if you added more hair around the ear area. also the background could've taken more time, but with the look of the actual person it draws away from the background.
All and all this is a work of great talent.. Good job!