Coliseum Morpheuon is level 16-20+, and ridiculously cool.
I agree. It's very, very cool.
One of the things I like the most is that it turns the tables on people who say things like "I can't GM for high level characters because the players use spells and items to break the game."
What makes this a work of genius, in my view, is that it takes on these charges seriously and solves them.