We watched 
John Carter this evening.  What can one say?  It's not as terrible as some would have you believe; not terrible at all.  I quite enjoyed it (although there was quite a bit of Basil Exposition in the middle third).  Spike described it as a perfectly watchable early-period science fiction, which sounds about right.  It is true that there's a rather 1930's cheesiness about it but it does look gorgeous.
It's not wholly original as a film (which is an understatement).  Let me think.  There's ...
- Star Wars (various scenes stolen directly from several films)
 
- Dances With Wolves
 
- Gladiator
 
- Flash Gordon
 
- Any number of John Ford Westerns
 
- The dog out of Up
 
- Cleopatra (the Elizabeth Taylor version)
 
- Superman
 
- That ridiculous fourth Indian Jones film
 
- A bit of Hammer horror meets steam punk Sherlock Holmes
 
- Tarzan the Ape Man
 
- Several cheesy episodes of Star Trek 
 
You get the point.  But you know, I've spent more than the $5.99 it cost us from iTunes to watch far worse.  If they made a sequel (and it clearly ended with a sequel in mind) I'd watch it.  Given the poor box office in America, though, I doubt that any of the other ten books will ever make it to the silver screen.