Just for the record, I liked this movie. I think that the movie flopped because the premise is rather silly by modern standards. Audiences aren't going to accept a swashbuckling story about rival kingdoms on the planet Mars. When the story was written over a hundred years ago this might have sounded borderline plausible.
However, take the same general idea and make it a long time ago in a galaxy far far away, and then it becomes more plausible.
Here is a link to my review which I recommend that you read: http://letsallgotothemovie.blogspot.com/2013/10/stories-where-flash-gordon-rushed.html