Visuals and sounds are really great! Despite the high (really high) mouse sensitivity, it gives a relaxing experience.
I needed several try to figure it out, but I've finally understood that constructing lines added other instruments, and most importantly that there is only six instruments. After that, instruments are removed forever. The guitars alone sound really great, but I would I like being able to put back the other sounds. Once every instruments are gone, creating lines does nothing. That makes confusing first experience: player move around, creates music, stuff happens, and suddenly it "stops" and all is left is the xylophone.
But as short as it is, it's really pleasant! Once I understood that I shouldn't mash the space key, I could savor the music created, step by step. A really cool game!