Beautiful photograph of a beautiful (and very natural) model. I think the lighting is good, the detail is adequate, and her hair is great. I agree with the other commenter, however, that perhaps the cropping is the least interesting part of this picture. If you turned the cropping horizontally, it wouldn't seem so claustrophobic. There is something about the cropping in addition to her head tilt that make it seem like she's in a box. :)
The only other thing I would do is bump the contrast, only because there should be a better balance of darks and lights in a portrait, and this is more and the dark side that anything.
Kudos though, I still really like this.
-- Critique Club