This is one of the images I see on this site that grab my attention and make me want to save it to my "Study Images" folder (which I never do without asking).
First, I like the flatness and geometry of the background - reminiscent of early impressionist painting. The balance of light and dark, with just a touch of muted color is intriguing. You're not confined by the standard width x height ratio and you use the extra real estate to advantage.
The lighting enhances the flatness of the background and draws attention to the subject, especially the eyes and textures in the t-shirt. Few portraits make me wonder what the life of this subject has been as this one does.
OK - so this is really technical composition stuff that I'm exploring right now -
Thirds (Golden Mean) isn't the only guide for subject placement - and in this case thirds doesn't work well. Golden Spiral (conch shell - Fibonacci progression) would work better if the crop was more traditional in a horizontal format - BUT
In your second square image, (after your small crop) the lines down from his hand, to near his elbow, and up through his shoulder and the pillow, form almost perfectly the 3 proportional "Golden Triangles" that contribute to pleasing composition. The angle of his face, particularly his chin, is nearly perfectly supported in the intersection of the 66% triangle. I believe your cropped composition is excellent, if non-traditional.
So, I got an 86 on that question on my Art II exam. Whatever.
I like this picture.