Electroplankton is one of the more creative video games I've come across. Electroplankton is an interactive music game where you can make your own music by touching the "plankton". There are several themes (i.e., one theme is more melodic than the other).
There are two modes, Performance and Audience. In Audience mode, you can relax and listen to an already arranged music number. In Performance mode is where you make your own music, however.
The game is quite fun and is a good time-killer, however there are some flaws. There is no way to save anything you created, so if you created the best musical number of your life--it's going bye-bye once your DS is off. Other than that, the game may get boring after a while for some.
I tried this, but I can't find it in stores anyway, but would buy it if I found it on the shelves.