Very well done. The skin tones are superb as well as the shadows and highlights, and everything seems to be in order perspective-wise. Nothing looks too big or too small or in the wrong position. I do think the hair could use a bit more detail... it looks a tad blocky. It doesn't really look like her hair is actually coming from her head, and the part that is flowing near her shoulder is too "perfect". Hair doesn't exactly do that too often. It will have the occasional strand out of place. Also the fabric over her breasts is bugging me. I wish I could explain what it is about it... but it feels off. I think part of it is that the whole picture is so smooth, but that fabric is jarringly rough. It pops out too hard.
Over all though, it is an impressive piece, and I would love to hear your techniques for painting this.