Utterly fiendish (assuming I was completing puzzles in the way you'd intended and wasn't missing easier options) and thoroughly enjoyable. Great work.
Very minor suggestions:
- Playing with a controller seems to be almost entirely fine, apart from the equivalent of the "E" and "V" keys which would hopefully be a quick win.
- I was getting some quite bad screen tearing which detracted from an otherwise very attractive game so if a v-sync option could be provided then that would be excellent.