You!

This is incredible work! I love that hand! Seriously, I can't even imagine trying to draw a hand in that position, even with a model or photo to reference. I think you pretty much nailed the proportions and anatomical details, as well as the shadows (although the pinky finger seems to be... almost cut off from the rest of the hand, perhaps due to the dark shadow you've added between it and the ring finger).

Traditionally you would be warned against having an arm pointing straight at the viewer (at least that's what I've been taught- if you want to create the illusion that someone is pointing at the viewer you are supposed to angle the arm down or to the side to avoid having to drastically foreshorten the arm), however I think you've done a wonderful job and since I love the arm covering the face, I definitely think you made a good choice in positioning the arm the way you did. 

The other thing that caught my eye was the hair, which is beautifully shaded . I love how the face and hand are so detailed in contrast to the chest and arm. It really pulls my attention.

Unfortunately I agree with KaizenKitty about the chest being a little off. This isn't too much of a big deal, as the more detailed portions grab my attention first, however I'm sure you're capable of fixing him up a little. A man with a face like that needs an attractive chest, amirite? Alternatively you could crop the drawing below the hand and just forget the chest, but I'm not sure what that would do to the overall drawing.

In all honesty this is a beautiful work of art . I shudder to think of the time invested in all that detail though!!