Just got home from John Carter.
Very, very impressed. Considering the usual issues you get when adapting something and the fact that this is a century-old story that's been copied a few hundred times in four or five formats, I think Andrew Stanton did an absolutely amazing job. Changes were made, yes, but I think they were needed changes and made the story stronger, overall.
It was fantastic. I laughed, cheered, and even got misty-eyed twice. Granted, one of them was when the film perfectly showed a particularly gory-yet-iconic image from the books (no spoilers). It might not win an Oscar, but ten-year old Pete was shrieking with joy for most of it.
When the lights came up my girlfriend turned to me with a big smile and said "We get to see this again on Saturday!"