I just finished re-reading The Golden Compass (AKA Northern Lights) by Philip Pullman.

Re-reading the book has lowered my opinion of the movie. Inevitably, a movie has to remove a lot of the complexity from a book, particularly complexity internal to a character, but in this case, I think the creators of the film over-simplified things. They also made a few odd choices, like changing the order of some events for no clear reason.

Probably the biggest mistake is the ending. When watching the movie, the ending felt vaguely un-satisfying but the overall movie had been enjoyable, so I brushed that feeling aside. After having re-read the book, it is clearly a huge mistake. The current ending of the movie leaves too many things un-resolved, particularly on an emotional level, and wouldn't have led well into the next film. The book's ending is much more powerful. Since the original ending was actually filmed, hopefully it will show up on the DVD version of the movie.