(Note for other players - zooming in in the browser window got things to the right scale so I could play!)
Neat little game - definitely a solid foundation! I liked the setting and the use of the underground (Circle Line - I see what you did there! ;) Some visual variations in the stations would be great (oh, and for edges I thought the yellow rail was actually an obstacle and was navigating around it *facepalm*)
The enemies caught me surprise and the speed of the ghosts made for a sharp learning curve. But also made it satisfying to level up. The teleporting bombs made for a little jump scare but could perhaps be tweaked to not teleport too close to the player, at least at first. Or perhaps add a little impact to bullets so they knock enemy back.
Good sign posting on how to get to the final boss - the player character continuing to mention the ticketmaster made me keep going back and... surprise, boss fight. Nice combination of previously fought enemies coming in and then new attacks (particularly the having tickets fired at you!) Some variation in the music at the point would have added to the dramatic showdown.
Overall a great little game with lots of potential - well done!