"John Carter" is horrendously under-appreciated.
Having not read the book "A Princess of Mars", I cannot speak to the quality of Disney's attempt at another box office mega-franchise as an adaptation of the source material. But as a movie in of itself, I found the movie incredibly imaginative, entertaining, and in no way an insult to my intelligence. I strongly recommend this as a fun sci-fi adventure film with strong Western movie overtones.
Since Disney's marketing department failed miserably to promote such a great movie, I am now going to have to the read the Edgar Rice Burrough's "Barsoom" series of novels to find out what happens to John Carter, Dejah Thoris, and the rest of the inhabitants a Mars that never was. Oh, cruelty that is literacy. My understanding is that this book series inspired future sci-fi writers such as Arthur C Clarke and Robert Heinlein (if Wikipedia is to be trusted, though the logic is sound). Even if a lot of fluff was added to the movie, the imaginative basis of the story is even nowadays a well executed stretch.
Watch "John Carter." Don't expect anything particularly deep in terms of exploring philosophical, sociological, psychological, or scientific/astrophysical ideas and notions, but don't expect these to have been completely ignored in constructing the fantastic world of Barsoom.