This was a really fun puzzle! The difficult took a sharp jump for the last map, and it would have been nice if you could have some undos as I missclicked near the end and had to start over. Also, I thought the beggining was a loading screen until I realised I had to click right, and there could have been a bit more fanfare for when the game was finished.
I could really see this being a fun puzzle game, and it would probably be quite easy to generate a load of levels procedually with a walker! I'd love to see more from it!