The restart key being 'R' and having no way to change it is a terrible idea. I can't tell you how many times I've hit 'R' to reload and restarted the level without meaning to. It's very frustrating. On a related note, the music doesn't reset when I reload the stage, so the music layers over itself until it mimics the sound of my pained wailing.
Other than that, good job. This game is a lot of fun, and I can't wait to see where you go with it.