Watched OOTP yesterday. Just going by the movie itself and not comparing it with the book (which I haven't read), it was easily the worst of the series IMO. Despite not having read the book, I could tell while watching that explanations and expositions were glossed over, if not eliminated entirely, and then Mrs Slayer covered several of the omissions on the car ride home from the theater.
For being the shortest film of the series (ironic, of course), it also dragged in quite a few places