The first book, "Princess of Mars," is a lot of fun. It's entirely brainless, of course, and racist, and misogynist, and Imperial, and all sorts of other things you would expect from this kind of book, from that period - but it's far better written, I think, than most other stuff of its type. What I mean by that is, it's not boring. The action is exciting, and the visuals are great fun. Don't expect the least bit of plot, characterization, or intelligence, though.
Interesting that everyone is hoping the movie is aimed at adults - why? The book is a kid's book. People read it when they're 12. Yes, it has lots of violence and nudity, but in that giggly non-realistic sort of way you get from comic books aimed at 12 year-olds. This isn't an adult book, and it shouldn't be an adult movie - it should be exactly what the book is: comically violent, over-the-top nonsense.