Simple, but beautifully realized gameplay mechanics, very neat visual and audio style with great attention to details (like circles bouncing, imitating real physical impact). The ricochet mechanic took me by surprise. I think it is a lucky find, as this seemingly insignificant addition (in terms of mechanics) instantly expanded possibilities for tactical puzzle solutions. Also I think that this puzzle is good as it is, but addition of music and story would have made it even better. Now it's nothing more than an elegant and delightful time-passer.