The more sections passed, the better the ending to the story, although the appearance of more people in distress doesn’t seem to depend on whether or not there was a 100% satisfactory resolution to the problem. They just pop up on the 3D city map, running around and yelling for help, until you touch them and spread a little more musical happiness. There are 19 songs in all.
Hardcore Ouendan masters might find the songs a little simple to begin with, since so little has changed since the original. But there’s a challenging difficulty level in which the beat markers disappear shortly before they’re activated. It’s stupidly tough.