Your shading skills on the knee caps and lower chest are just wonderfully captured.
There are a few things I would like to point out; The foot appears to be quite 2D, (considering this is a 3D piece) and almost flat as if looking from above, I would suggest some darker undertones on the floor to create shading. (even if there is no lighting, etc as this will help the 3D effect). The face is also quite flat, as if there is no lighting or shape to it, in comparison to the rest, especially considering the detailing on the neck.
Some suggestions; A great idea would to be keep a little A6 notebook in your pocket and sketch, sketch, sketch, as you obviously have some beautiful potential clearly shown here, however I think these minor details are a tiny let down because I can see how much effort and time has gone into this piece. I also like the fact you've used a blue background (if intentional or if there was an actual blue background), I would also try a variety of colours including greens and purples so not to inflict any compromisation on the tones of the body (which obviously can include red).
Please keep up the good work and I look forward to seeing more of it in the future.