First, that's a tough shot to pull off on the Metro...so easy for people to be standing in the aisle and blocking that view. Plus the lighting in the cars sucks (unless you're out of a tunnel).
Second, what a great composition. To me, the background isn't the background, it's a critical part of the photo...that juxtaposition of the crying baby with the woman tuning out with headphones.
Nicely done.