This is top notch design technique, it should be used as an example in a classroom setting.
The line quality is very high. The lighting really gives it that 3D feeling as well as the edged lines that spiral into the backround (the rock cave is very implied) even the little pebbles have lighting.
What is most important are how many different types of lines used, the viewer can easily distinguish objects.
Putting this into a 3D program would be fun, because it already has such a great structure and can easily be brought into a wire frame.
Design textbooks might even pay to reference this.