This movie stumbles badly right away. There's no real need to update it, it works better if it isn't updated. But that's not the real failing. The scene where he is in the hospital being told by some mad scientists that he is being sent to Mars as some sort of science experiment was one of the most absurd that I have ever seen. It was unintentionally comic. Why in the world did they need to declare that Barsoom isn't Mars, but a planet in another solar system? Yes, we know that the real Mars isn't like the Mars that Burroughs imagined, that doesn't interfere with the story.

There is a scene were he asks for something to drink, and he is given a rag full of sweat. Another scene where he asks for food, and he is given the excretion of some larva. Neither of these are in the book; they eat something that seems like cheese or tofu, and to drink, they drink the liquid of a cactus-like plant. Why they chose to make this change is beyond me. It seemed to be an attempt to disgust the audience, and didn't make the movie any better.

A good Phantom Edit would cut out entirely the portion before he gets to Mars. A minute of two of narration at the beginning could replace the entire first part of the movie. It would also be necessary to snip out the part where you learn the bad guy is from Earth. You don't have to eliminate him entirely, just the nonsense of him being from Earth.

I'd also delete the scenes where he is given sweat and larval excretions to drink.

Other parts are more minor. Traci Lords is a bit too old, too clothed and too blonde to be a plausible Deja Thoris. She seems more a cranky sitcom mom than a princess of Helium. The tattoos on John Carter seem unlikely, a tramp stamp on a man? But these are minor, the major flaws of this movie are overwhelming, but if they were cut out, this would be, well, not a great movie, but not too bad.

If you watch the movie, you see that throughout the movie, one of Tars Tarkas' tusks wobbles. A fairly minor thing, but it shows how quickly they made this movie was made.