I'm not a huge Matt fan, but I really enjoy this artwork a lot.
I enjoy the pose which is natural and relaxed and the character, background and objects all work with each other - nothing seems forced in the composition. The closed eyes and cigarette really add to the character of the artwork. (I also personally find shoes very difficult, so I'm very impressed by those too!)
The light from the window and the light from the monitor are both done really well; they provide a contrast to each other with the natural light so bright in the window against the wave-like blue artificial light that gets overpowered. Perhaps the light outside could have been made even more intense.
My areas to work on would be: the left hand appears to be larger than the right. The computer looks a bit sketchy compared the rest of the work - perhaps more work on the colouring/shading of it. I feel as if his groin area is twisted slightly too far towards us (although I may just have been looking at it for too long now!).
I really enjoy the sparkles up by Matt's face, I feel as though they're enhancing the blinding sunlight, but I'm not sure about the ones further away, such as bottom right. It doesn't seem to be adding to the environment nor an emotion. (Without it there'd more of a dark/light contrast)
I think overall the execution and composition are really lovely and I certainly find it a fascinating and relaxing piece. Just perhaps a couple of edits could give it more impact/contrasts.