I like how the game conveys the idea of each musician finding his right spot in the flow of composition.
Great minimalistic approach — it's harder to do than it may seem.
Not sure if it needs more gameplay elements or not. On the one hand it's freedom from all the usual gamy elements like goal and challenge and that's fresh. On the other hand the process of creating actual gameplay meaningfully attached to music may bring you to absolutely unexpected discoveries.
Correlates with me so much — my current long term project is heavily influenced by free jazz.