If I wanted to tell you what genius is, and if I wanted to tell you in the form of an anime, I'd make you watch Bakemonogatari. You think I'm joking...
"Genius" is the only word I can find to describe 15 episodes of: absolutely exciting yet perfectly casual dialogue, immensely over-the-top characters which are awesome regardless, and a surrealistic plot and setting that doesn't describe what the world's like, but what we imagine it to be (or something like that).
As I already said, "Genius"...