I'm not sure I can really put my finger on why I was so "meh" on the movie.
I do know that part of it was the human civilizations on Mars that I am supposed to care about. Um...no, fuck humans, this is Mars goddamnit!
Also, the (non-titular) Princess was the primary reason there were so many problems. That being said, even if she had married him the bad guy still would have caused trouble. But really, she kept talking about "sacrificing everything for her people" and then didn't do that.