Guitar hero or DDR for your DS.
Simply... The world has problems, and the Agents are there to make things right, with a beat. Everytime, they are there to cheer up the "main actor" with the right song. As for the gameplay, quite simple. A number appear on the screen with a cercle shrinking. When the cercle overlap the number, tap! Sometime there is long line, that require you to tap and follow that line.
Simple right? Yeah. But so damn hard when you come closer to the end of the game. Your score if multiplicative to how many touch you manage to do in a row. So, when you start, you will score in the 50 - 70,000 points... But when you do a perfect song, you can go in the millions!
Aside from that, the game is perfectly tuned. It's smooth and really responsive for this totally new type of gameplay for a DS. Sure, the DS sound quality is horrible when used with the normal speaker. If you buy this game, be sure to have a good headset. The graphic are all 2D aside from the selection screen and the dancing agent. It has a kind of manga style that copy nobody else.
This game is, if you have a DS, a must have!