It never occurs to me that you can consider most books go to the renderer in order to be adapted for the screen. Usually, the process is somewhat disturbing, and if you know the book upon which the movie was based, you'll find a thing or 2 you had hoped to see, but were cut out of the movie. With long books like the Harry Potter novels this is naturally something to be expected.
My kids and I have read all of the books more than once, and the main problem we have with this movie (and most of the HP movies after the second one), is that aside from parts of the story being omitted, new content has actually been fabricated. Considering how much material was not used in order to make the movie a reasonable length, we have yet to find anyone who can explain why new content was fabricated at the expense of original plot.
I realize this movie has been out forever, and most people have seen it, or at least have seen the trend the movies leading up to this one in the series were taking, but I think you should know you just get snippets of the story, and presented with a lot more doom and gloom than is necessary. I think that you are better off listening to the audiobook of this, as the reader does such a great job that you feel you are actually watching the movie. Except it is better.