1. The Harry Potter films
Don't get me wrong, I love the Harry Potter movies. However, nothing touches the books. There's just too much of the books left out of the movies for me to really love them; the books far exceed their cinematic counterparts.
2. The Lightning Thief
Bad. Bad bad bad. The plot was wrong, the characters were wrong, it was wrong. Don't even get me started on the fact that they made a sequel of it, "the mist comes out of a spray bottle." ?? Read the books people.
3. The Golden Compass
Also completely terrible. I don't even remember a lot of this movie because it was so not the book and horrible that I think I repressed it. At the very least, it certainly left out most of what was in the book.
4. The Lord of the Flies
They just did this poorly. For one, it seemed like they killed Simon with glow sticks, so I'm not sure how that was accomplished, but then Piggy's death scene was just... bad enough that it was funny.
5. The Shining
Even Stephen King, who wrote the book, hated the movie. The whole point is that you're not supposed to know what's going on with the main character, whereas in the movie, he was just crazy. To quote my mom, "it just lacked the subtlety of the book".
6. Interview With the Vampire
Tom Cruise.
Mostly, the casting in this was just bad. It was pretty watered down from what the book originally was.
7. The City of Ember
