+1
A lot of material has been changed for the movies to tell a movie story (a story that continues from film to film). The moveis are good by themselves, but they are not the books.
Using one film per book is not at all wrong, but things are altered or left out. The Goblet of Fire was altered quite a bit to make the story more life-or-death serious. The dragon scene was not supposed to be life threatening in the book, but the film tells a very different story. The skrewts are not in the film at all, and although they may not seem important, they do connect the story in terms of the students and what they have been doing all year to the end (that sounds general, but it is late right now). The maze in the film was just odd, actually seeming like a less threatening version of what is in the book. Still, the film story was fine. Dobby is just forgotten about.
One could make a case for two films for the last book, but, in agreement with others, that would not be necessary. Two films would build suspense and manufacture desire to complete the films, but it si really needed? A lot happens, but is it any more than the fifth book or even the first one? The point is that more of an effort should be made to create a better film (not films), which may dictate a longer running time. Done well, long movies are just good movies: done way off or slightly askew, a long film is waaaay long.