I think this is a terrific photograph and even more so for not being enhanced.
I agree with the above comments but you asked for comments and critique, so these are my thoughts on how I would change the photo (see mod).
I cropped higher up so that it is above the elbow rather than leaving a stub of an arm below it - this is general rule - crop above a joint, not below.
I cropped in a little from the right to make the image more left of centre rather than on the left.
I do not thin think having two strong light sources on both sides works well. It may be been that you were trying to backlight the hair and it has spilled on to the front. I think this detracts from the impact. So I darkened the left hand side with a dark grey layer on soft light in CS3. I liked the way that it actually seemed to enhance the back lit hair.
The other thing to watch is women's arms side on - it is a lot of flesh. To minimise it make sure that there is a tiny space between their arm and their body - it stops the arm from spreading side ways.
I think it would be better if she had lifted her head like a sting on a puppet and brought her left shoulder back a little. It would probably have reduced the amount of flesh showing on her back which I think detracts from her face. I tried to simulate this by using liquify.
I have a mod available if you wanted to see
My suggestions are only minor changes and are always easy to make - so much harder when you are on the spot and under pressure.
Fantastic photo and looking forward to seeing more.