I know a few people who did not go into this movie prepared - they didn't remember the plot of the book, they hadn't seen the previous movie in over a year. They did not enjoy the film. I recommend either re-reading the book or watching the previous movie before watching HP HBP. The book is long, and the film's screenwriter had to leave out a lot from the book. The film's pacing is fairly fast, so you don't have time to catch up if you are already behind. There are three scenes in the movie that are significantly different from the book, one of which differed in a way that didn't seem necessary, and that was disappointing. However, the film was still highly enjoyable. The actors keep getting better with every film.