Ninety-Nine Nights is probably most well-known for being the game produced by Q Entertainment's Tetsuya Mizuguchi - the man behind Rez and Lumines. The demo weighs in at under 600 MB, and will give players a chance to play the game before it hits retail.
The game didn't exactly set cash registers alight in Japan (but what 360 game has?), but it's expected to perform a lot better when it's released in North America in August. There's no official European release date, but retailers seem to think we'll see the game in September.