Yes Lucas is right Frank its could use some more dark shadows. The only thing is I don't like dark shadows and that's the reason that I`m not a good figure painter. Maybe some folds could just a little more shadow but I`m always afraid to ruin my work if the shadow`s are going to dark.
Use washes then, if you dont want to use oil colors. GW washes work very good for example, made not too good experiences with MiG and Vallejo (but maybe I used them wrong or so). GW is a "fool-proof" thing. Your decision of course (ask 5 people and youll get 8 different answers!).
Agrax Earthshade would work best here most probably. And if you find the effect too strong - thin them with water.