I was looking forward to seeing these types of shots in this challenge, I really like them, and I find this a good one. Very emotive. Strong composition, and a perfect splash of light to make the point. Nice job.
Although I like the light on the upper half, the slight bit of light at the bottom where the leg is doesn't look right considering the almost completely black middle half. Perhaps full use of the 640 pixels would have helped in terms of detail, because a lot is lost with the smaller size. As for the model's expression, it doesn't look "dark", but it probably is just the lack of detail from the small resolution.
I liked the concept. As I look at the picture, I think it would have been more powerful if you cropped more of it out. I like the upper right part of the picture, to about midway down the frame.