Screw you! Princess Bride was awesome! Then again, I've never read the book, so I can't compare.
If you're going on films people think are awesome, but they're actually terrible because they're really bad reflections of the book, I think the award has got to go to:
My Sister's Keeper
*Spoilers below. Highlight if you want to read.*
So, it's the tragic film about a young girl called Anna who was basically created so she could donate her blood and bone marrow for her sister Kate who has cancer. Anna is told she has to donate a kidney to Kate, but instead she hires a lawyer to sue her parents for the rights to her body, which would mean she'd never have to be a donor for her sister again, but also means her sister would die. After loads of falling out in the family, it comes out that the only reason Anna didn't want to be Kate's donor anymore is because Kate told Anna that she wants to die. In the end, Anna wins the court case and her sister Kate does die of cancer. It's a very sad and touching movie and I thought it was awesome!
Then I read the book and discovered one of the weirdest book to film adaptation fuck ups of all time... They killed off the wrong sister. In the book, Anna has just won the court case and is in a car, contemplating her own future and it's implied that she comes to the decision that she wants to donate her kidney to Kate, even though she doesn't have to. Right after that, Anna gets killed in a horrible car accident. All her organs are donated, her sister Kate gets the kidney she needs and survives.
It's a shame because I'd probably still think the movie was awesome if I didn't know how the story was supposed to end. The story of a young girl dying of cancer was really tragic, but it completely missed the point that the book was trying to make, that people were so busy focusing on one sister that they failed to realize the other sister was equally important until it was too late.