Elite Beat Agents
Have you ever wanted to travel around, helping a small group of secret agents with serious dance skills mysteriously influence events by hitting the right beats? Of course you have! And Elite Beat Agents lets you do just that. This is the sequel to a Japanse game called Osu! Tatakae! Ouedan, and fits all kinds of Japanse stereotypes. There is big hair, a giant city-wrecking cat (Meowzilla, of course), and ridiculous situations from an oil tycoon discovering Atlantis to an attack by music hating aliens. And yes, it is as fun as it sounds.
The gameplay is carried out mostly via the DS touch screen (various stuff happens on the top screen, but on any difficulty above the easiest you won't have time to watch the top screen). Basically, little numbered circles appear on the screen, and your job is to tap them in order and on the right beat. If you do so, the agents dance accordingly and a bar at the top (I believe it was called a groove meter) gets a little better. If the groove meter gets too low, horrible things happen to whoever the agents are helping (shown via mini-cutscenes), and if it reaches the bottom, you lose.
Now, fair warning - this game is HARD. However, it does difficulty right and offers something for everyone. The first difficulty mode, Breezin' is more of an introduction and it is hard to do poorly. Cruisin' gets a little bit harder, and the third difficulty level, Sweatin', becomes pretty crazy. On Sweatin' you can go through a whole song without missing a note and still lose, because you didn't hit them precisely enough (each note is worth between 50 and 300 points if you don't miss it). After every song you are given a letter rating, and despite having played several songs with no misses, I have yet to get an A, let along the top rank of S. The final difficulty, Hard Rock, lets you play as the Elite Beat Divas (listen - as a 23 year old male, this isn't the kind of game I play in public very often), and is insanely hard. If you like a challenge, this game is for you.
Elite Beat Agents is everything a rhythm game should be - it's addictive, fun, exhilarating, and has a good selection of songs (at least some of which almost everything has heard before). Sadly DS games are getting harder to find, but this one is a gem and worth tracking down if you're a fan of rhythm games, dancing, or Japanese-style zaniness.