I thought the last song was fun, but I didn't like that you had to press random buttons on tune to defeat Ursula. That didn't amuse me, but like I said, the last song was the most fun!
One thing I didn't like was that once you unlocked the world, you went there, but had to learn new abilities to do the songs. It was kind of a nice break from fighting, though. I didn't particularily like it, though.