Okay, first of all, It is amazing. Technique skills with cross hatching is flawless. What I think would make it even more amazing is add some water colors to it. Like,use the blacks, grays, etc. it will look amazing! If you don't want to mess up or just want to experiment, try making a copy, or get tracing paper, and shade on the tracing paper to have a comparison without making official changes. Or you can actually keep the tracing paper. You can do different layers to produce interesting effects. You should try it out and keep up the fantastic work!