Adaptations are tricky business, particularly when you tackle the classics. There's just no way to meet everyone's expectations. If you adhere too slavishly to the source material, you risk creating something turgid and lifeless; it's impossible to shoehorn in every part of the novel without having things drag on and on and on.
The other extreme, which I personally find far more frustrating, is the case of the writer who seems to have perhaps skimmed the text, then pillaged it for whatever bits and pieces he found most interesting, creating a largely new story and slapping on the old, well-known title.
Why, hello, Dracula.
