I really liked John Carter & I think you will too! I'm a big fan fan of John Carter of Mars & the movie does it justice. I may be slightly invested in having other people see it, on account of how I would sure like a trilogy to be made; I figure it only as to do as well as Tron: Legacy, right? Let me hit it with a couple of broad strokes, just tick off things on my mental list. First, the Green Martians are really well done. I think they are a triumph; Willem Dafoe & Samantha Morton as Tars Tarkas & Sola really seem like giants with four arms, in a way that isn't intrusive to the flow of the story. I should say, they seem like giants with four arms that are also people which is the real trick. That was a big success; all the bits & pieces of the movie with the Tharks are great, from the eggs to the arena. The Therns-- the White Martians-- are a great villain, with their "we use religion to control people" angle being handled well, along with a sort of sinister shapeshifting & worldhopping. Mark Strong has a similar presence to his role in Green Lantern, only this time with his menace fully embodied, & with a movie that actually gives him other characters to play off of. Taylor Kitsch is a fine Carter; I know people really like him from Friday Night Lights & I hope that broadens the audience for this movie. Lynn Collins as Deja Thoris was also pretty compelling; the script bulked up her role from the books, & for the better. She is no shrinking violet in the novels, but that element of her character is on display in the foreground of the movie, & is coupled with a new scientific bent to the character. Which brings me to the screenplay itself; it is really more of a new John Carter story, with the skeleton of A Princess of Mars used to support a largely original story.
The biggest change is the introduction of a MacGuffin; the Thern's amulet. It is the device that causes John Carter to leap between the worlds...which is sadly much more mundane an explanation than in the books, in which John Carter just...dies at the beginning & the end of the story? Much weirder, much more interesting, though the misdirect at the end at least gives it a purpose. The best thing about Chabon, Andrews & Stanton's writing is the sense of humor; there are an awful lot of laughs in the movie. Starting with the completely canonical pratfalls when Carter arrives on the Red Planet, moving on to him being treated like a mewling Green Martian pup-- with some strange Martian milk being used as the deus ex machina for why he can start understanding Martian, which works for me, as the books' narrative handwave is just "telepathy"-- & then on to lots of crashed & crashing fliers. That use of wry slapstick really works in the movie. Oh! & I was worried about the "secret weapon" the villains use-- another MacGuffin is a bad sign-- but it is really actually quite clever; it is the Ninth Ray! That totally works, & the involvement of the Therns moves it firmly into solid ground as far as the narrative framework is concerned. The special effects really work on an organic level; Woola the Martian "dog" is like an über-Archie, & has a lot of character, & as I mentioned, the Green Martians are fully successful as characters. Jenny winced at one point, saying the greenscreen was bad, but I didn't see it; I thought the aerial chase in Zodanga was a little bit too CGI but that is a very minor complaint. Overall, I really liked it. There are some pacing problems, but once it gets rolling it doesn't stop. Maybe we'll get lucky & the Sword & Spaceship genre will get big?