The background setting looks very nice. Could use a few imperfect bricks or a poster/sign or something to liven it up a bit though.
The character's arms look weird, because they shouldn't start so thick like that at the top, thin like that at the end. Shirts don't usually go from baggy at the top of the sleeves to tight at the end, and the hands seem too small. We should see his thumb (or at least space occupied to give the impression that he has thumbs) if he's got his arms to the side like that. Or I guess make his shoulders broader, and make the the arms 4px instead of parts starting at 6px and moving to 5px to 4px.
His elbows seem too low. I think that shadow should start about two pixels higher.
The legs also suffer. It goes from nice curves to boxy cubes at the botton. The black outline shouldn't be broken up like that. Instead add new, slightly darker shades if you want to define the forms.
Lastly, where are his feet! It's unlikely that shoes are the EXACT same color of brown, so mix in your other palette colors when shading the shoes. Since it's a face-on view like that, not top-down, his shoes should also occupy more vertical space.
Hopefully this helps.