Edgar Rice Burroughs wrote his series of John Carter novels before space flight was more than a fancy. This movie is more adventure and romance and very little (if any) actual science.
This movie is the best production of A Princess of Mars, the first story in the series, that I've seen.
If you're a fan of the John Carter novels then you will probably get some enjoyment from John Carter. While there are some differences you'll meet some familiar characters and recognize quite a few relevant plot points.
Not a great film, but not a bad one, either.