a think the skin is a bit too saturated and yellow, a peacier tone would probably be more appropriate you could also use much more contrast in your skin palette. he's clearly shaded from a distinct direction, but the highlights don't conform to the shapes I'd expect to make him up. where's the chin/neck? when using greys, it's often best to sneak a little saturation in and tint them slightly, so they're not as boring to work with.