I enjoyed playing with my 7 key piano! We made some nice little bits of music and almost accidentally broke into a bit of Dr Dre.
The concept is great and original, the trouble I had is that I know so little about music that I felt I needed more guidance. For example, I made someone happy once, someone sad once, and someone happy again. However - I wasn't really sure what I did to invoke that response. I wonder if you could put some note progressions / chords or something to that effect on the screen to help your player explore different sounds and learn the impact of them. Then afterwards, a more free-style game play approach would work better.
Really nice and relaxed game for the pacifist jam, thanks for submitting :)