One the lessons I learned early on from Jay Maisel was to look for gesture in photos. Small, large, implied, etc. but it is this gesture that can move a photo from good to great.
The trains in Japan are fun to shoot as they all are a little different and it seems we are on them every day. Still looking for my classic "mega full people smashed in during commute" shot! My guess that one will be full of gesture.
Pro Tip: Need to shoot these on manual with a shutter of 1/15 or so with an F10 set up. With this slow shutter speed and no tripod you have to shoot a bunch to get a few that rock.