It's a nonsense! They took the longest book, and turned it into the shortest film. It felt at times like I was watching one of those "Previously on..." clips, it was just scene, scene, scene, bish bash bosh.
I honestly cannot tell how somebody who hasn't read the books can gain an understanding and appreciation of the story, given the amount of back-story that goes unexplained in the films.
Presumably it was down to WB wanting the minimise the spend on OoTP, but surely the success of the movies leaRAB to huge profits, it isn't like they are taking a risk on a film that may bomb.