Haha, this is a pretty fun idea. Old MacDonald's got a bit of a jazz feel to it for some reason? Maybe because that third note is a little on the flat side. I actually kind of like it.
As for the game, it's a quick sitthrough and the challenge is just in the completion. I like how the notes will only play when you shoot them, however, some of the themes - particularly the Tetris one and Lavendar Town - were practically unrecognisable. Perhaps because of the limitations of the staff, but it might have been more ideal to keep to simpler songs that are more recognisable to make it more engaging. Ah well. I did enjoy it overall.