This Book is amazing, It seems like I can retrace the current direction of my interests back to that book which I read like 2 years ago. This book will teach you how to think. The only way to describe it is insanity to the nth.
Illuminatus is my favorite of Wilsons books to read, although I think his two most important are Prometheus Rising and Cosmic Trigger I
Tips for reading:
Like Roadrage said, keep a notebook handy, if nothing else just write down the names and a few notes of the characters, because there are so many (they are still being introduced halfway through) that it is totally overwhelming trying to remember all the names.
Too many people give up reading this book because they cant get unconfused. You WILL be confused while reading it (especially the first time), but you are still learning alot (trust me). Eventually you will get a feel for the the fact that you cant really get the feel of this book
Just dont give up because you feel like you are too lost to continue.