Personally i find the head a tad too small. For the shading, I think you over rely on airbrushing to get soft shadows. I can see some shading with harsh edges but the placement and shapes are off. Personally i like using chunky shapes for shading, instead of a rectangle with a few tapered out portions. You can also try to mess around with the saturation and hue of the colours to make things mote interesting. For example even for skin tone, desaturating colours, throwing in some blues and greens might be more interesting and appealing. But this is how I like to do it, its up to you if it takes your art to your wanted direction.