This is absolute genius - I love it!
I share Vospi's Z,X,C confusion, but that's not a crucial thing.
A bigger thing for me is that I wish there was an option to play without the timer - I got stuck on a level and got really frustrated working through earlier levels I didn't remember the solution to. I guess next time, I'm going to have to go old-school and write the solutions down on paper! :)