Haha, personally my favorite Potter films are the ones that have the gall to actually be a film, so Cuaron and Yates' installments, because they focused on the essential elements of the story instead of padding random details that would work in a miniseries but bog down a movie. That said, they do not miss the whole feeling of the source. I have no problem with changes as long as the themes or ideas behind a novel are translated well, otherwise what's the point of licensing something other than gaining notoriety from the built-in audience? Make it your own, but to a point.
Unless you're doing the 1852598345th version of something, or you're turning pulp trash into cinema gold like Jaws or Psycho.
I loved books first, so debate with my all you want, that's how I feel.