You clearly have a grasp of proportion and anatomy. I especially like the way you drew the folds on the lower part of the trouser legs. My only critique is the footwear mainly on his right (our left) foot. The proportion seems a bit off. May I ask what references you used for the shoes? (perhaps think of drawing/studying many shoes in order to develop a visual library if you haven't done so already)
Also may I ask what reference you used for the pose if possible just want to make sure if there's anything else I could spot. (Otherwise the foreshortening of his arm looks fine and if there's any 'mistakes' I can't spot it's then it's not obvious)
This is a nice piece, definitely looks as if it could fit in Grand Theft Auto and the colour scheme is perfect.