I'm just now scanning the first roll from the Mamiya. As suspected most close-ups are way off due to parallax shift. Oops. I gotta get me one of them parallax adjuster-thingys.
On first glance I'd say the Mamiya does indeed take better photos than the Great Wall. I'm sure the lens is of better quality blah blah blah but I'd also say that part of the advantage is the super-clear viewfinder. I can actually see if I'm focussed whereas with the Great Wall I had to sorta-kinda cross my fingers a little bit.
To exemplify what I mean, my brother took one look through the Mamiya viewfinder and exclaimed, "That's clearer than life. Fucked up!"