Firstly, this book is easy to pick up and read. Some reviewers suggest that you should try other works first, but I don't see why this should be the case. The story is quite involving and complex (as an idea), but the actual writing style and explanation is clear and very well described. Eldritch is coming back to earth and quite what he has with him, and whether he is still human is up for debate.
As you read this book, you almost go through all of the deadly sins and their impact on human life - someone is trying to upgrade their beauty or their intelligence (vanity), a co-worker is trying to take your job (envy), the boss is sleeping with the consultant (lust) - Dick plays out the story against a backdrop of impending doom, with the present-day prophet of the universe about to set up a new world based on his own self, a self that is alien, obnoxious, and without a true soul. The interesting twist to the story is the fact that we are all a part of this monstrosity, and perhaps Dick was ultimately trying to lay out the process by which the mind loses itself. I read somewhere that Dick could never actually read this story again, and never checked the final draft as it scared him.
For such a doom-laden book, it is remarkably upbeat, and the central figures have a lot to like in them, and a distinct sense of purpose even in the most trying of times. Towards the end the fight against Eldritch mounts, and the all-knowing nature of the new god is put into question. Everything is a question with Dick, and all is never lost.
This is classic sci-fi, and highly recommendable.