I've been on vacation the last week, and the Illuminatus! trilogy (in one volume) is one of the books I got for the trip.
I'm a short way into the second book, and I think it's safe to say this is one of the weirdest books I've ever read!
I was really annoyed with the habit of changing character perspective and time period until I got to the end of the first book, when it all seemed to make sense. But then the second book took up as if the end of the first book were not an actual explanation of the weirdness, so I'm back to not knowing what the fuck is going on.
Boiled down, reading this book is a lot like reading trip reports of nutmeg experiences (having no experience with, or interest in, said experience.) Random and chaotic movements through time and paranoid thought processes.