http://www.ropeofsilicon.com/article/film-adaptations-and-their-source-material-how-faithful-should-they-be

I'd like to discuss yet another editorial from Brad Brevet (I promise, this will be the last one...probably), this time on the issue of adaptations. It goes without saying that the greatest challenge of any adaptation, especially a cross-medium one, is remaining faithful to the source material while leaving one's mark on the adaptation to avoid a tedious rehash of the source. Although discussing film adaptations as a whole, Brevet does take some time to focus on those of the Harry Potter series, namely the latest film in that franchise. He defends the changes in said film, with the assertion that, "When it comes to the Harry Potter films I have a hard time believing someone like 'Anonymous Friend' could be happy with any of the films released so far. None of them have stuck strictly to the narrative".

Overall, I agree with Brevet's sentiments. None of the Potter films are what I would call the epitome of outstanding cinema, but I would strongly argue that they all accomplish what they set out to do (aside from make millions of dollars): offer up a visual and cinematic rendition of Rowling's novels. Whenever you're adapting a particular work from one medium to another, there's far more to it than simply getting all the details and plot points nailed down. It has to be tailored to the medium you're adapting to. Furthermore, the adaptation must capture the spirit and overall mood of the original work. That's the real key to a good adaptation.