Hey all! \o/
I've been told about the game Osu! Tatakae! Ouendan! in Neo-Geo.com forum.
It's a music game for Nintendo DS, it was released only in Japan.
I saw some videos and I got so addicted with the video that I bought the game!
And my opinion is: BUY IT NOW!
This is the best game release 'till now for DS!
It's damn addicting! The musics, a total of 15, are great ones!
Here are some videos:
http://media.ds.ign.com/media/746/746980/vids_1.html

The game has 4 levels, the first 2 ones are available at the start. Once you beat the level 2, you get the level 3, and once you beat level 3, you get level 4.
Game is hard at level 2, very hard at level 3 and impossible at level 4!
Really, it's a "MUST HAVE" for any DS owner!
It's in Japanese, but it's very intuitive. You don't need to know any Japanese (like me) to understand the storyboard.
Really, consider buying this game soon, it's hell worth it!
^_^