In order to do the final book justice, I could see why the movie was shot in 2 parts. The movie follows the book well, but assumes that you are familiar to the plot, and can understand what is happening next.
I went along with my 7-year-old son, who understood only part of what was happening, but was entertained nonetheless.
I saw this in 3-D IMAX, which was incredible. I recommend this one in theatres.
I have read all of the books in the series and I feel that this has done a lot to bring in most of the story lines. Overall, it was well-made and stops in the appropriate point (where I would have separated the story if I were writing it in 2 parts).