Very nice work. ^^
The bricks look a bit tiny with him in front of it. I’d suggest removing the drop shadow on the wall, to make more space between it and him - that would fix the potential scale problem. Although I really dig the cool way you’ve drawn the shadow. =)
In the closeup the nose looks a little lopsided, but then I looked more closely at the reference picture. O_o’’’ I would personally make it more symmetric, but I’d say it’s your call.
For a full-quality portrait it’s a little detail-less, but for a character painting that’s not meant to be seen in closeups, it works.
The background texture is really nice. The only thing it lacks is some lighting to further define its surface texture - at the moment if feels a bit flat. But if you’re making textures for 3D these would probably be added as a bumpmap afterwards.