
So much of this movie was actually from The Two Towers. But I guess this makes sense, as the three movies were made together. The entire section with the spider was from the middle book. Also, in the movie Frodo actually abandoned Sam. This did not happen in the book at all. Frodo was slightly suspicious of Sam when he asked to share the burden of the ring, but he never told him to go home.
I honestly was bored for most of the battles in the book. And although they were spectacular to watch in the movie, and the special effects were great, I got a little bored with the battles in the movie as well. The army of the dead was pretty cool though.
The novel has over a hundred pages left still after the ring is destroyed. I really felt like that whole section was anticlimactic. The movie went on for almost 30 minutes after the ring was gone, but I felt most of the material they kept was fairly important to wrapping up the story. (Frodo and Sam saved by the eagles, Sam marrying Rosie, Aragorn crowned king and marrying Arwen) The movie left out the entire 'battle for the Shire', and showed the Shire just as it was in the beginning. I agree with this decision. With the destruction of the ring, it seems most harmonious if all after that is good, not evil.
I wonder if the fact that Frodo did not willingly give up the ring haunts him in the end. To me, it seems like it would, but neither the book nor the movie seem to give any indication that this plays a part in his unrest in the years after the Return of the King.