Somewhere between DDR and Guitar Hero, but better.
It took me a couple tries to figure out how the button combinations work, but it's really the 4 directions and 6 2-button combos of DDR, plus the Strum Bar from Guitar Hero, arranged in a colorful rainbow circle, with great music and an awesome stop-the-aliens-from-invading-earth storyline. It's hard enough to keep my trying to improve my score without being impossible (except maybe in that "insane" mode).
10/10 and 5/5 because I can't think of anything this needs, (I know I normally hate Strum-Bar-like mechanics but this game works exceedingly well with it and can therefore get my full-points review) plus the animation is great and the music is well-synched.
And for those of you who don't get it, you have to hold down two buttons for many combinations, hold the strike key for centipedes, and strike on the beat of the music wherever possible.