Wow ! This is an extremely intense picture that, to me, has two main strengths: the model and the light. As often in a great shot, each strength need the other one to exist, and this is, I believe, exactly what happens here.
Let's start with the model. Her pose is stunning, very dynamic, very dramatic. The drama is reinforced by her muscles and body lines, which add lots of depth and details to her overall beautiful shape.
These depth and details are highlighted in an extremely efficient way by the lighting used. Each curve, each muscle, each bump and depression is carefully outlined, stressed, reinforced. The model seems to fear that light, and this impression is strengthened by the light itself.
Finally, the grain used adds a touch of authenticity that renders this image extremely real. It looks like the model had been locked in the dark for a very long time when that window suddenly opened, in the very moment caught by the photographer.