What's your vote for the worst movie made of a good book?

There must be so many. One which springs to mind is "The Witches of Eastwick" - John Updike. I loved the book, which is weird and wonderful and intelligent. The movie is just stupid, although Jack Nicholson does make a good devil. Another would be "Dune"- Frank Herbert. Legendary book, fairly lame movie, although I did like Sting as one of the Harkonnens, forgot the character's name now. I have to keep reminding myself that a movie is a separate creative entity from the book which inspired it, and that the director is entitled to make whatever changes work for his/her medium. So good but different movies have been made of good books.

Dragonlance. by Margaret Weiss and Tracey Hickman. There was a badly made cartoon movie of this series. Thankfully, they only made one.
Ender's Game is another bad movie that comes to mind.
The Hobbit.....I loathe the Hobbit Trilogy movies.

Practical Magic
Exit to Eden

Both unrecognizable.

A couple that spring to mind are I Am Legend and Abraham Lincoln: Vampire Hunter. The latter was a fun secret history romp of a book while the movie was a dumbed down CGI-laden splatter-fest. Ho hum.

In the former, instead of the realization that comes to Neville in the final pages of the book, the filmmakers decided to create a HEA ending filled with hope for the future, thereby completely missing the point of Matheson's story. I do give some credit to Smith's acting though; he did ok with the material he was provided - but the writing and CGI were both fairly bad. The Omega Man was not as far off but also was not a great adaptation. Charlton Heston's hammy acting didn't help either. Vincent Price as The Last Man on Earth came closest to the book, which is not all that surprising since Matheson was involved in writing the screen-play for that first adaptation.

Meanwhile, over here in Oppositeland, a terrible book that was turned into a much better movie is Forrest Gump, IMHO.