I am compelled to write this based on the extraordinarily misleading review below. If you don't already know what this is, DON'T buy it. Not only is it not a novel, it's not even a story. Come to think of it, it ain't even, strictly speaking, a "book"! So if you're looking for an introduction to Philip Dick, you should really try something else. Most of us start with Blade Runner.
To explain, toward the end of his writing career, Philip Dick had a visionary/religious/mystical experience. Like all such experiences, it was exceptionally difficult to verbalize, rationalize, or explain. If the experience itself didn't drive Dick mad, the task of making sense of it clearly did, at least for a time. Dick entered a period of heightened creativity, struggling to give voice to his religious experience through writing. Dick called this process, and the body of text it produced, his "Exegesis." Traditionally, the word signifies the process of expounding upon and interpreting a work of literature, typically a religious text; here, the object of Dick's literary critique was his own mind.
This book is a relatively narrow selection of pages from that effort. It reads like a philosophical journal, and consists of outlines, correspondence, doodles and rambling essays on science, creativity, ancient history, religion, death, and drugs. This is the raw ore of genius, but it is extremely unrefined. Worse, it has an eerie "tinfoil hat" feel to it; one gets the strong sense that Dick was flirting with mental illness. The casual reader is certain to be alienated, and unnecessarily, since the Exegesis formed the basis for several excellent works of narrative fiction. VALIS, Dick's crypto-autobiographical novel recounting the same events is infinitely more accessible.
But, if you, like me, are more than a casual reader - if you have read Valis and Ubik (and possibly Cosmic Trigger I: Final Secret of the Illuminati to boot) - if you take seriously the possibility that Dick contacted a divine intelligence in February of 1974, then this book is for you. And if that's you, then the content will speak for itself.
But the editing? In my view, it's above average. Since I have never seen the file cabinets from which these pages have been selected, I can't attest to their completeness. However, the stuff that's here is consistently engaging and seems to have been selected with care. Better still, the text has been annotated by a multidisciplinary team of editors, ensuring that the reader has a guide for some of Dick's frequent digressions into brain science, Biblical hermeneutics, and pharmacology.
This is much better than I'd hoped and the serious fan/student will be very, very happy.
[UPDATE: In a previous version of this review, I complained about the absence of explanatory material on Bishop James Pike. A comment below pointed out that there is in fact a detailed entry on Pike at the back of the book. My mistake. My gripe is withdrawn.]