Art (drawings, shapes, anatomy, etc) alone is actually decent (for the most part, gets a bit dodgy at points), but the lack of shading/shadows makes everything look too solid, flat, and static... Which is not only boring but a bit of a pain to look at.
Good shading and shadows can give a soft look and shapes e.g. on thighs for softness, and on the face for shapes (shadow that shows nose and lips shape). Also for textures on clothing and other objects. Even if it is for minimalistic details it works very well, like Tokoharu's stuff http://dynasty-scans.com/chapters/evening_rain or the recently uploaded http://dynasty-scans.com/chapters/hiyori_geta
Shadings and shadows are key.