Music and the atmosphere is relaxing and nice! I didn't like the fact that you "tail" hitting enemies killed you as well, I thought it more as a movement particle, but that does increase the difficulty, but I would try it that only the main ball would be the one that can get hit.
Otherwise a really beautiful game! As someone mentioned before some kind of best time would be a good addition and then randomising the diamonds and creating new levels would make a good mobile game that people would definitely buy.