Well, I don't want to brag, but I made my own full Rhythm Heaven game idea. It's pretty much like Megamix, but it's not. If you want to view it, you can click the link below. But it's okay if you don't, to be honest.
http://rhfanon.wikia.com/wiki/Rhythm_Heaven_Starshine
One of the ideas for the game is a game called: Concert Blues. Now, I don't want to brag, because, to be honest, it's probably not that good of an idea. But I may as well put it here, because it is a game idea I personally enjoy.
Concert Blues: You play as a boy performing for a concert full of zoo animals. A cowbell will play once, then another noise plays before the audience in the background starts clapping. You need to press either the left or right arrow keys to match in time to the beat. The noise will be a high-pitched horn for the left beats, and a low-pitched horn for the right beats. A ding will let you know one beat before it's time to stop. In addition, there are two additional cues.