Short review: if you haven't seen the John Carter film yet, do so ASAP (if you have already seen it, you probably don't need an excuse to see it again).
Slightly longer review: John Carter is a highly enjoyable action-adventure romp, a fun Summer popcorn film that just happens to be released in the early Spring, the type of film that really benefits from being seen on the biog screen. Drenched in pulpy/swashbuckler goodness, it is evocative of action films from older eras, the type that Hollywood doesn't make too often these days: if Douglas Fairbanks or Errol Flynn had made sci-fi epics back in the day, it would be something like this.
The story is based heavily on Burroughs' first Mars novel A Princess of Mars, with a fair chunk of The Gods of Mars (the second Mars novel) and a bit of The Warlord Mars (the third Mars novel) thrown in for good measure. This may not please Burroughs purists, but overall, the changes work, and work well (Dejah Thoris is a much, much stronger and more interesting character here than she was in the original books).
Is it perfect? Of course not. There are a few nits I could pick (I would have liked for the red planet to be a little more, well, red), but nothing that seriously hindered my enjoyment of the film. It's a good film, one that deserved better marketing from Disney, and could do without negative reviews from film critics who trash it out of hand (as so often happens to sci-fi films that don't purport to be deep and meaningful).
Don't believe me? Check out my friend Greg's passionate plea on why you should see the film, as well as Erik Kain's piece on why you should ignore the critics who are trashing it.
And finally... I really, really want a Woola. Damnit, Disney, where's my Woola toy?