Grab your rotten fruit.
Bestselling books have an annoying habit of going to Hollywood where they end up looking like a forty year old woman with too much botox and sparkly, hot pink lipstick. In the real world, this would make me secretly sympathetic, but in the writhing mass of producers/writers/actors/cameramen/scorers that live in my DVD case, I consider all adaptations to be fair game (unless your name is Hayao Miyazaki or Tim Burton and you are taking utterly senseless but charming liberties).
The cellulite sagging, twinkie stuffed celebrities facing off in each corner today deserve at least some measure of respect. Both dearly beloved, but each with a score to settle, one with a reputation of cheap, emotional porn, and the other accused of the dark arts.
Twilight has the roughest time. The book relies on its angsty, first person point-of-view to sell you on its personal form of sparkly crack. Movies on the other hand, are shot in omnicient POV which means poor Kristin Stewart spends a lot of time sitting around trying to infuse lots of backstory and emotion into a series of looks. Mostly she just looks constipated.
The movies feel lazy, like the actors depend on their hotness to carry the story (which is shortsighted considering there's no way any normal human actor can look as hot as Stephanie Myers vampires).
Which is why Harry Potter wins this round. It also had a hard job this last movie. Since the story only covers the first half of the last book, they were forced to make a blockbuster without the golden carrot of resolution to offer the audience. That and the last book is dreadfully dull in the middle, with Harry, Hermione and Ron wandering around in the forest arguing with each other for chapters upon chapters.
Lord Of The Rings gets around it by making everything as visually stimulating as possible. Harry Potter and the Deathly Hallows gets around it by having Emma Watson. (that and a super talented group of musicians scoring the film) It was the first movie where I realized the music was making me feel whatever emotion would normally be communicated by internal dialogue in a book. Brilliant.
I know Harry Potter And The Deathly Hallows isn't even close to the best example of a film score being used to communicate depth, but when you compare it to all its peers (bestselling books that have been turned into mediocre movies) you find yourself actually understanding and sympathizing with all the teenage drama instead of being annoyed by it.