Valis

"Horselover Fat's nervous breakdown began..." These 1st 5 words of the book set the stage for everything to come, literally. The remainder is a delusional discourse on the nature of reality and how it relates to God and religion. It takes the reader into the mind of a schizophrenic in all its pathological glory. When looked at that way, it can be quite entertaining, whether you want to regard this as a semi-autobiographical version of PKD himself or not.

From pink lasers to the brain to "Christian Gnosticism" to homoplasmates to the tractates (PKD's condensed exegesis), VALIS is nothing if not interesting for all the weird and fantastical ideas it contains.

Do not make this the first PKD you read, since I would have just dismissed it out of hand and never finished it if it was written by any other author. You need to have some background with both some of his other works and the man himself before this can at all be appreciated.