A mish-mash of themes and ideas in this book with occaisional flashes of brilliance but never quite weaved together as expertly as he has done elsewhere.
Themes explored in this book include those that he has examined in other books such as simulacrums ("Do Androids dream of Electric Sheep", "The Simulacra"), what it means to be alive and mental illness/breakdown ("A Scanner Darkly").
Certainly the focus of the book seems to shift from the former to the latter which leaves one with the impression that the author didn't really know where he was going with this one. I don't know if this is one of those stories he just sat down and wrote it down as it streamed from his head but it certainly feels like it.
Definitely worth a read though (indeed I am yet to read anything by Dick that isn't worth a read).