Mines going to be like guitar hero. In the way that you have to time hitting the icons, but your performance will determine plot. you could replay the game a bunch of times and continue getting different endings, and to beat it you have to get all the endings in an achievement type window. Once you do that you can skip around the levels, and such.
I may even make a secret undocumented (possibly alien related) secret ending.
All the music will be piano by my family.