It won't appeal to the US crowd as much, but fans of EBA will love this game.
The Bad: Less songs than EBA; not as tight of control as EBA either; way too Japanese for some people; costs around $50, while EBA is around $30.
Osu! Tatakae! Ouendan came out in Japan before Elite Beat Agents ever existed. Many people decided to import it when they feared it would never make it stateside, and for a good reason - Ouendan is an infectious, weird, funny, and well-designed rhythm game. It's just kind of hard to recommend now that Elite Beat Agents exists and appeals much better to a US crowd.
The setting in Ouendan is a bit different from that of EBA. It is, obviously, set in Japan, and instead of an agency that dances to help people, it is a male cheersquad. When people are in need, they yell "Ouendaaaaaan!" and the dancing trio come in to save the day. Just like in EBA, the game is controlled completely by tapping, dragging, and spinning on the touch screen, and it works just as well. Fundamentally, Ouendan and EBA are the same game - EBA is just localized and changed to make more sense in the US.
It's hard to recommend Ouendan mainly because it costs upwards of $50 to get your hands on one, and even though it doesn't require comprehension of the Japanese language, it sure would help raise the enjoyment level. It's just that the game, the setting, the characters, and everything are all very Japanese, and it's aimed at a Japanese audience. The J-pop tunes probably won't appeal to many Americans anyway.
So, overall, those who are interested in this kind of game for their DS would be good to stick with Elite Beat Agents, which is a little bit slicker and has more replay value and songs anyway. Also, EBA will only cost around $30, so you'll save cash.