Overall, a great shot. Subway cars are indeed, difficult to make interesting. This shot pulled me right in, which is more than I can say for many of the pictures floating on the critiquable page that are low-quality pictures of cats or something.

Anyways, the photographer here has a great feel for lines. The lines of the chairs, the rails, the segments in the ceiling, all draw you towards the back, where there is one lonely passenger. Of course, this also isn't simply black and white. The contrast has been changed by my best guess, and it creates a far more dramatic, and grungy picture, adding to the overall feel.

It's a great shot of a difficult subject. Well executed. It's been done before, but in my opinion, not this well.