While I do like the expressions on these two characters, particularly the one the left, and the colors arrangment is interesting, the proportions are a little wierd. the heads are just a little small, and the brown-skinned girl's mid-section looks like it'd snap under the weight of that pair.
Additionally, the brown-skinned girl looks like her left shoulder is bruised for some reason, and the lighting around her crotch doesn't seem to be consistent. The high-lights on right thigh should be to the viewer's right, since the highlights on the rest of her suggest that the light source is to her left.
All in all, not a bad echi/fanwork piece, but not amazing.