Sorry to bring this up. I saw the FOTR shortly after reading the book (2000-1).
I remember the reaction of some of the movie goers who have not read the book was "Huh? Is that it?" when it was finished. They didn't seem to understand that it was the frst part of the trilogy.
I think that the movie worked well by itself without any prior knowledge of the book. I have read the book and found that it added to my understanding and appreciation of the movie.
I had read part of the Hobbit a few year before and it was good to see Gandalf!! 🙂