I love clean line art.
Doing it with a Cintiq and PS has its ups and downs. I find myself carving the lines with 1 finger on the B and the other on the E, rather than actually trusting any long fluid strokes.
It takes a lot of time compared to just diving right in with paint and sculpting the light. For me anyway. sometimes I paint it first (in B&W) then add the line.
Each line is so basic yet contains soo much information that even the tiniest change in it alters the whole shape of the composition. Sometimes I am unsure of how somethings looks and have to experiment for the right line to add the proper depth or whatever this can take patience.
That and my lack of experience is the big time consumer. I am experimenting way too much on stuff I should have down in a few strokes. Oh well...
Practice, practice, practice.
Peace