A totally unique experience, something everyone must try once
The gameplay is similar to other music-based games, in that you have to press buttons in time to the music. The way it differs is by having symbols representing the different buttons (spikes, waves, blocks and loops) which can be combined into one (such as a spiky block or wavy loop), which is where it gets complicated, as the game is so frantic it is sometimes hard to work it all out in time. It is frustrating at times but great fun, and perfect as a take-it-in-turns party game, as it will make a mockery of anyone's gaming abilities.
What is also special is the use of graphics. Looking at screen-shots, you would be excused for thinking that they look terrible, but it a choice made by the developers, not a sign of laziness. The simplistic look helps place more focus on the game itself, and the graphics get more sketchy as you lose health, essentially making the level into a health bar. The animation is fluid and clearly had more work put into it than one might think at-a-glance
So if you like Japanese games (or even if you don't), give it a try, it won't fail to disappoint you.