We had a very similar idea but went a slightly different route with it. I really like the angle you went with and the art is fantastic. The only thing I would say is it would have been nice to have some sort of map although trying to figure out which station is which might be a big part of the fun. Maybe I missed it but if the stations had an indicator of what number they are on the station itself, that would make exploring a bit more fun. So you wouldn't have to enter the station to find out.
Otherwise, I loved it! Very solid entry for the amount of time we had. Nicely done.