Take one part Monty Python and the Holy Grail, one part deconstruction of Broadway tropes in general, a dash of local references (especially Seahawks, natch, and the fact that gay marriage is legal here in Seattleish), a lot of broken fourrth wall, and just a pinch of audience participation in the form of "Always Look on the Bright Side of Life," which is from a different Python film altogether: The Life of Brian..
Because it's Monty Python, it is of course a bit shocking in spots, because British humour and American humor are... different. I have trouble imagining an American play getting away with a song like "You Won't Succeed on Broadway (if you don't have any Jews)."
But it did have most of the best parts of The Holy Grail (although I don't remember seeing the "What is your name? What is your Quest?" bit). The Knights Who Say Ni! and Tim the Enchanter and the Black Knight and the bit with the coconuts and the swallows were all there. Oh, and the Rabbit and the Holy Hand Grenade, of course. Oh, and "three shall be the number..." and the monks with the books to their heads.
Now, I never ever buy stuff at these things; I don't get the soundtracks or the super playbills or any of that, ever. But I did this time; I got a Black Knight plush (with velcroed-on limbs) and a Killer Rabbit plush. Because yeah, I'm a dork.