Dan Schindel’s review:
It's fun pulpy goodness. Pulpier than orange juice, even.
John Carter (of Mars) has a sense of playfulness and good humor and adventure that's rousing and infectious. It really does feel like a turn-of-the-century dime store novel.
Kitsch is alright as Carter, but it's Lynn Collins who steals the show. Her and every CGI character in this film. Tharks > Na'vi.
Unfortunately, it's hobbled by really weak villains who have some of the vaguest motivations ever, boring and unnecessary bookends on Earth, and a plot that's generally scattershot and amorphous, and threatens to lose you at multiple points.
Basically, everything you've heard about this movie is true. Both the good and the bad.