Hey, that's a great piece: it has a very nice light, tons of character. You could bring out few things, strenghten the contrast, but after a second thought, I like your calm, balanced way of painting. There's only one thing out of the harmony: his face is YELLOW. That's a rare skintone, and it stand out from the rest of the model. You've done great job painting that face: very nice shading and (as anthonyw said) it is full character. It would be pity to spoil that, but the hue is much to striking. Maybe bringing out metal part on the front of the model using yellow colours will lessen the contrast. Nevertheless it's a great mini.