To understand Tull, you must have a incredible working knowledge of English history and folklore.
To listen to BOC, you must understand the abundant references to high ritual magic [courtesy of the ever-odd Sandy Perlman], science fiction [Michael Moorcock], HP Lovecraft, general 'collective subconscious' mythopoeia and world history.
I'm surprised The Butthole Surfers isn't on the list, considering.
Even Type O Negative forces you to consider the implications of their word play and entendres.
Even though The Doors are on there, I'd bet the stoners are listening but not comprehending.
Sheesh.