I watched John Carter last night. Not as bad as the reviews made it out to be, but then again I am a sci-fi nut. The film suffered from some poor pacing and tension building, along with a lack of focus in the middle and a poorly edited beginning, along with feeling like some 1950's sci-fi books I've read (like the Dominic Flandry books), which isn't necesarily a bad thing. As to be expected with a summer blockbuster, the acting was pretty much of a bargain basement quality, but the princess made nice eye-candy.
If you like sci-fi, I would rate it 7/10. It was a perfectly enjoyable movie to spend an evening watching. Otherwise, probably a 4/10.