I usually don't make comparisons between book and movie. I appreciate that they are different works even if they stem from the same original story (from a book, usually) and I don't hold them up and point the things that are made different. There is beautiful stuff out there that completely twisted up their original story (like How To Train Your Dragon or Howl's Moving Castle) and still made great films.
But I couldn't help myself with this one. I mean, they did screw up. They re-wrote a story that was pitch perfect ready-made for the big screen, seriously, one can read that book planning movie scenes (much like the last Harry Potter) but they went and made it into a silly fireworks show with nothing to give for. And why would you change the end of a story if you plan to produce the sequels!? *rips hair off* It makes no sense at all. It was just sad.