The Road by Cormac McCarthy.
Saturday by Ian McEwan (and Atonement isn't much better).
My Sister's Keeper by Jodie Picoult
The Boy in the Striped Pyjamas by John Boyne
Most Dan Brown books - I've read 3 and they were all disappointing.
Bloody Twilight.
Definately Ulysses - man thinks about his penis for 700 pages and we're supposed to like him because he feels some vague affection for his wife despite having no other redeeming qualities whatsoever.
How to Be Single
The Great Gatsby - it wasn't bad, exactly, it was just nowhere near as amazing as it was billed to be.
The Stand by Stephen King. Took Deux ex machina to a whole new level.
Like several others have mentioned The Essex Serpent was disappointing.
The Sense of an Ending by Julian Barnes.
A Little Life - there was some beautiful writing in there but the story became tedious torture porn at points.
The Goldfinch had an intriguing premise but could have done with some heavy editing.
Sepulchre by Kate Moss. After the mess that was there's no way I'm reading another of her books.
Anything by Charles Dickens but most of all Bleak House. Or possibly David Copperfield. Can't decide which is worse.
I wasn't keen on The Lovely Bones. It most certainly did not live up to the hype.
The Alchemist - I was expecting to be blown away but it was all hype and no insight.
Having said that quite a few of my favourites have been mentioned in this thread! Each to their own!