What is the worst and best book to film adaption?

We all have favourite books....and we all get a tad worried when we hear they are about to be adapted to TV or the big screen...it could turn out very bad..or the film could be even better than the book.

What is your worst and best adaptions..?

My favourite are..Game of thrones, Dexter, True blood, The green mile, LOTR, To kill a mockingbird..

My worst are..The Harry Potter films..(I love the books..not crazy about the films) Lolita, Enigma, My sisters keeper, The Dark is rising, East of eden...

That's all I can think of now..What is the worst and best book to film adaption?
The Harry Potter films are disappointing (to fans of the books), because each book is simply too long to be adapted into a single film. As a result, they try to condense everything, and it comes out looking rushed and abridged. Much of the joys of the HP books comes from the lush detail in Rowling's universe, and much of that is lost in the films.

Another book has failed on screen several times is "The Great Gatsby", but for a different reason. The novel is a great read because F. Scott Fitzgerald was a great author. His prose is wonderful. (Just consider the last few paragraphs of the book, as one example.) The plot, on the other hand, is relatively trivial on its surface. The joy is in the reading. So when they turn it into a movie, all that comes across is the somewhat banal plot, while leaving all of the poetry and color behind.

"Dexter", on the other hand, is better than the books on which it is based. Which is quite an accomplishment.What is the worst and best book to film adaption?
The only one I know and love is "Tres metros sobre el cielo" (Spanish version of the movie) . The movie is greeeat!!!