Portrait from Steve McCurry's work

I love Steve McCurry's photography, especially this one even though it was an extra challenge. Any tips will be greatly appreciated!

Reference:

First sketch:

Begining shading:

Shading done

The face turned out much rounder than the reference and the eyebrows got screwd up along the way, but here it is!

April 2nd, 2016 Update:

Worked on the shading further. The skin texture definitely improved, but the eyes ended up a bit cartoonish. Starting to get a handle on the value shading though!