Two quarters

This a truly beautiful work of art. the line art the coloring, the shading. You have some very good skills especially in the skin tones. A lot of time and detail went in to this, I can tell. Every detail was skillfully executed. From the strands of hair, to the winkles in her clothes. Even the shading and light placement is perfect. I see almost nothing wrong with this painting except for one thing.
While the face is very realistic, it seems almost out of place if compared with the rest of the body. This might be due to the fact that your lines are way fatter then they need to be. The lines on the face are thinner and make the face look more realistic. While the lines from the neck down (mostly around her legs arms and stomach) are so thick they give this piece a more cartoonish look. It clashes badly with her face and makes the whole thing look inconsistent. You do the same thing with your other portraits.
I suggest that you either make the lines thinner on the body or thicker lines on the face.
One more thing that doesn't have to do with your drawing skills. I would like to remind you that deviantart is art sharing website that now has a lot of artist under the age of 15. This portrait and all your other portraits are very risqué and could be deemed inappropriate. I think you should put them on a mature content on them. There are other more adult sites where you can post art like this with out trouble.
Other than that, like I a said before, you have amazing skill and great technique.