There's a demo for it available on the eShop.
Anyways, I played it when it first came out and enjoyed it. From what I hear the sequel, Theatrhythm Final Fantasy: Curtain Call contains all of the songs from the first game, so if you really want to try it out I'd suggest going the extra mile and pick up that instead.
But like I said, there's a demo. It's the only demo I have around 5 hours on actually, haha.