Hollywood always seems to think they can make a classic book better (huh?) or more accommodating to its teenage male audience since, surely, no one else goes to the movies anymore. Take a look at the Flavorpill list. What other movies would you add?
I'd add five more classics:
The film adaptation for WATERSHIP DOWN (Richard Adams). Awful animation.
The film adaptation for WAR OF THE WORLDS (H.G. Wells) with Tom Cruise.
The film adaptation of THE HOUND OF THE BASKERVILLES (Arthur Conan Doyle) Any version. I've yet to see this classic story filmed properly.
The film adaptation of DESIRE UNDER THE ELMS (Eugene O'Neill). Sophia Loren and Anthony Perkins? In what universe did this make any casting sense? Cringe-worthy.
The film adaptation of DRACULA (Bram Stoker) with Gary Oldman. Unwatchable. Give me Bela Lugosi any day of the week.
...and while we're at it: VAN HELSING (based on Bram Stoker's character) with Hugh Jackman. Unwatchable doesn't even begin to describe it.
These aren't the worst regular book to film adaptations, mind you, just the Bungled Classic Book-to-Film Adaptations. I'm going to post my own choices for all time worse adaptations one of these days.