Quick and simple: I like the line weights and the colors you chose. I think this is well balanced in those areas. The colors are very vibrant and bold!
Don't be afraid to explore with more contrast. Contrast will help in the depth of the cape/cowel area. It will also help in the mouth area. A little darker in a little more areas and lighter in others. You added a hard drop shadow in the lower right corner, more of that treatment followed throughout would be good, like right under the mask, where the cheeks show through. Some lighter blue could be added to the eyebrows to give more depth. If you want to get fancy, try adding another light source, it could even be a different color.
$5.00 is a bargain for this! Hope this helps! Keep it up. San's artwork is perfect for this kind of work.