Subway

I'm pretty proud of this, though the orginal was better (just too light).
I drew this in the subway on 33rd street, I think i probably worried a few people, i doubt they normally have kids come and sit for an hour on a bench staring at a corner and drawing. Still, I'm pleased with it, I feel i got the depth right, which is a first for me.
Darkned somewhat in Photoshop.
I hope you like it, please comment critically I'd like some help improving my sketching.