John Carter of Mars is based on the book - a Princess of Mars by Edgar Rice Burroughs. It's a very enjoyable film and in some respects improves on the original tale. The film's beginning roughly follows that of the book. There are discrepancies, but I think they make for a better film, and lead nicely into the next installment, Gods of Mars. The book is a remarkable tale, given that it was written so long ago (early 1900s). Edgar Rice Burroughs also wrote Tarzan and given how many films that generated it shows that Burroughs' plots have an enduring quality.
I would recommend the film to all fantasy fans. It is visually stunning. The story is good and the interaction between Dejah Thoris and John Carter is handled well, but not as the love at first sight, as in the book. The CGI is terrific and the creatures are a faithful rendition of those in the book. The tharks and white apes are great. Captain Carter's ability to leap great distance, and strength, due to the lesser gravity of Mars, is explained in the film - but I'm not sure how well this will be picked up by those that haven't read the book. His strength is handled with some humour, especially having to learn to walk in the lower gravity.
I only hope they make Gods of Mars, which in my opinion was the better book. Please support this film as otherwise other films in the series will not follow. Well done to Disney for making this film. It was great fun!