Hrm. It could use some differentiating values, to make it have more depth, especially if you were going to for realism. Realism relies more on value to show its shapes than on outlines.
Also, when colouring, it tends to look better if you keep making your strokes in the same direction, or if you at least keep it flowy-looking, rather than colouring one way, then going an entirely different direction right next to that.