For me there have been three books I can safely say I didn't enjoy at all:
Things Fall Apart - Chinua Achebe - Just could not get into it. I know its all to do with African culture, but I just could not relate, their strange rituals with foo-foo yams and beating the wife and kids for acedentally dropping a bowl I just could not see point in. But then again, I think thats my western culture kicking into it.
Snow Falling on Cedars - David Guterson - I found the prose in this cold and distant, the dialogue stinted, and as a reviewer rightly said on Amazon: 'The characters are about as alive as my left shoe'. The plot I found uninteresting too, and jumped around too much.
and
Devil Wears Prada - Lauren Weisberger (Is that her name?) - The pinnacle of silly chick literature. I read this purely to pretend I'd seen the film of it with a friend and not the gory modern Australian adaption of Macbeth. Most of the novel is about a young woman who goes to her work, gets paid big bucks but whines the whole time about how her boss treats her. I spent the whole 3/4 of the novel I read thinking: 'Why doesn't she just sue her boss for harassment and defamation? Better still, change jobs? She could put the richest fashion mag job in her resume.'
Ahh, the joys of flaws in bad plots...