One book that had a huge impact on me was "The Illuminatus! Trilogy" and when I meet others who were first introduced to the subject matter covered in that book, it had the same impact on them. I suppose if you already knew all the stuff the book covers then maybe not so much. But then I had already ready Pynchon's "The Crying of Lot 49" and everything Lovecraft ever wrote and it only heightened my enjoyment of the Trilogy so I don't know. That book also quote a bit from Ishmael Reed's "Mumbo Jumbo" so I hunted that down and read it too. I lent it to a guy on my ship who had also read the Trilogy and "Crying" and we would discuss Mumbo Jumbo for hours.