Theatrhythm: Final Fantasy was the first game I bought for 3DS. If you like Final Fantasy music or rhythm games, it's a wonderful time. If you like both, it's a meditative haven.
It's getting a huge sequel, Theatrhythm Final Fantasy: Curtain Call, that is coming soon to Japan. Dale played it at TGS and found it to be more of the same great Theatrhythm, but with over 200 songs, 60 characters, and music from Type-0, Advent Children, Final Fantasy XIV.
A demo for Curtain Call recently hit the Japanese eShop and Nintendo Life has video of the three tracks from it. I can't wait.
First Impressions: Theatrhythm Final Fantasy: Curtain Call [Nintendo Life]