I hated Ubik until I got to the last few pages, when it suddenly turned into one of the best stories I've ever read. There's a great twist at the end, the details of which I've since forgotten so I can't spoil it for you.
I find PKD a bit of a difficult read sometimes because he obsesses over irrelevant details like outfits or tech to an irritating extent, but leaves out the wider context of the environment he's created. You can tell that he has this incredible, rich, fully-detailed world built up inside his head, but he doesn't let you access it in the same way that somebody like William Gibson would.
Maybe I should give Ubik a re-read and see if that ending stands up to the memory impression I have!