Really clever interpretation of the theme! I think this would work really well with some sort of rhythm aspect tied to how the blocks change, similar to a lot of those levels from recent 3D Mario games. That, plus tightening up the controls a bit would make this something I could totally see myself grinding out levels on riding the subway or something!
Also, one minor design critique is that there's no disincentive to keep bouncing on green zones to max out your health, but I can't think of a good solution to that problem, and given the time constraint there probably wouldn't have been a chance to implement one anyways.