I'll admit, I'm a sucker for sonar-based gameplay (once made a fully-dark-but-with-sonar asteroids), and this is a pretty good implementation of it. It's a shame death means resetting the whole game, because I didn't quite feel like redoing the first four levels after dying (and the noise covering the screen was getting a bit unpleasant). But until that point I had a lot of fun attacking the darkness!