Probably because I'm very old school in photography, and I also like true B&W, not PS colour images, for me this is one of the best images I've seen for a long time, it's simple and pure; basically a great portrait.
If I had to critique it I would say that the light behind and above her makes it look like she's having a, albeit small, idea. I'd also suggest the top is cropped a little just to bring her higher up the frame and away from the centre.