I read these books as a child and reread the first two before seeing the movie. Although the credits list this as an adaptation of "Princess of Mars," there are several elements from the second book incorporated in the film to give it better context and a sense of closure. Great special effects - my wife and I both enjoyed it. Some of the elements of the book were "updated" for a current audience, like the use of the 9th ray for teleportation. All in all, this is a great action movie that was unfairly panned by critics. (Think: those who can, do; those who can't, get jobs as critics.) Good fun.