There has never been a movie adaptation of a book that didn't receive irate criticism from fans of the book. But movies and books are different and have to satisfy different criteria. In most cases, remaining strictly faithful to a book would result in a worse movie. Poor adaptations are those which change stuff arbitrarily, just because the screenwriter or director or executive or star didn't like it the way it was - but even these can make good films, sometimes better than a faithful adaptation would have been. Good adaptations are those which try to remain faithful to the spirit of the book, while making changes that make the material work as a movie. The LOTR movies fall into the latter category, IMHO. There are some things I don't like about them, like most people. But they are about as good an adaptation as you could realistically hope to see.