Very nice, using the full available size probably would have helped. The shadow on her right eye is a bit dark and her nipple being slightly cropped hasn't helped. Great tonal range, nice looking model and pose.
Ouch sorry but the nipple ring caught my attention. Too me, the nakedness doesn't create any extra emotion other than "ouch". I think that you could have achieved a sexy effect really by just focusing on her face. Her eyes and expression carry the mood.
This image would have benefitted from greatercontrast. I would also look at the tutorial called 'Pimp those eyes', that with some dodging and sharpening would have improved the image.
good naturally lighted portrait, though the crop is a bit tight (and the image too small:). Might have been helpful to use a reflector from her left to brighten her hair a bit.