Think of it like this: Imagine the sights and sounds of Times Square on New Year's Eve. The huge canyon walls of skyscrapers belch confetti from their windows, the voices of the teeming mass of revelers countdown into the new year. While holding that idea in your mind try to imagine being in another, very quiet place: an ancient Buddist temple, or the serene interior of a magnificent cathedral. During any given 420bpm session, you might hear something New Age, something Classical, something orchestral, something old and primitive and something high-tech, all of it unified in a way that gives it the sound of successive states of mind.
Or, you can think of it like this: there was a house party at 420bpm's studio and all the world's musics were invited. Metal got drunk and started a fight with Jazz in the kitchen. Classical tried to intervene but, after being rebuffed, joined a soul-searching conversation with R&B and Funk over in the den. New Age was braiding Bluegrass's hair on the bean-bag chair, while Drum & Bass, Country Acid House, and Tuvan Throat Singing went outside to look at the stars.
420bpm makes different musical styles into characters in an unfolding drama, and allows them to relate to one another in ways that sound like what music sounds like when we daydream about it.