I liked this a lot, it's beautifully made and every penny of that massive budget is on screen.
However, one of the problems with adapting such influential material nearly 100 years after it was written is that lots of the good bits have been pilfered over the decades by others (Star Wars, Flash Gordon, Superman, Avatar, errr... the Chronicles of Riddick). During the film you get the strange feeling you know it already even if you haven't read the book, like I haven't, which is a massive shame.
The protagonist himself is somewhat bland, the excellent support cast have transported in from Rome and the most interesting character, Lynn Collins' Deja Thoris, isn't used nearly enough, hinting at an intriguing back story but relegated to Red Planet Rapunzel. I think I'd prefer to see less John Carter of Earth and more of a Princess of Mars...