One of the worst reading experiences I've ever had was with Philip K. Dick's A Scanner Darkly. I loved Do Androids of Electric Sheep and was expecting to really enjoy A Scanner Darkly, but I absolutely hated it. The main characters were just too Beavis-and-Buttheadedly stupid for my tastes. The sci-fi elements -- the scrambler suit, for example -- were the only interesting part of the novel but they felt arbitrary, as though they'd been tacked on to a boring real-world memoir of life as a wastoid as an afterthought. The experience has made me hesitant to read more of Dick's novels, though I'm sure that sooner or later I'll recover from the trauma and check out some of his other work.