Locus magazine has put two very good reviews of John Carter on their Web site. The first, by Gary Westfahl, says a lot of things that I have said in my own writings, but more elegantly (http://www.locusmag.com/Reviews/2012/03/barsoom-revisited-or-forewarned-four-armed-a-review-of-john-carter/). I found this paragraph to be particularly striking, where Westfahl describes the plot change to make the Therns provide Carter's method of transportation to Mars:
This change is particularly ruinous to the film because the power of Burroughs's original story, after all, lay in the fact that it represented the ultimate in wish fulfillment: you look up at another planet, you transport yourself to that planet, you find that you can beat the crap out of everyone and everything around you, and you marry a beautiful princess and become that planet's Warlord. This is the story that inspired many people to become interested in space travel, like Carl Sagan, who related how he as a child, after reading Burroughs, had similarly looked up at the stars and dreamed that he might be transported to another world. Significantly, he did not dream that he might somebody run into a powerful alien with a magical device that could take him to another world; it simply isn't the same. And this sort of story must end with the complete, transcendent triumph of the hero, something that the film's John Carter is denied: no matter how long he remains on Mars, the film suggests, he will always be gazing suspiciously at every person he encounters, fearful that he or she is a disguised Thern plotting his demise. Perhaps this was justified in story conferences as laying the necessary groundwork for a possible sequel, but one might respond that Burroughs himself, after nervously providing his early novels with cliffhanger endings, began giving his novels complete, satisfactory conclusions, confident that he could always devise some pretext for one more sequel without any obvious hooks; and certainly, Hollywood itself has never failed to find some way to keep a profitable franchise going, even contriving to produce three more sequels to a film, Beneath the Planet of the Apes (1969), that ended with the complete destruction of planet Earth. In sum, since Burroughs's novel already offered a sufficient number of dastardly opponents, there was no reason to add the Therns in the first place, and every reason to remove them in the final, chartreuse version of the script.The second is a conversation between Howard Waldrop and Lawrence Person (http://www.locusmag.com/Reviews/2012/03/howard-waldrop-and-lawrence-person-review-john-carter/), both of whom mention some of the same points I've made but with the added benefit of Person claiming no emotional attachment to the source material. I've read a lot of reviews in the past few days, and it's a stroke of luck that perhaps the two best I have read thus far are on the same Web site.