I agree re the Russian cams, plus the Medalist... But imagine paying Leica/Contax prices for essentially the same functionality...
With Pentax, I will be heretical: I love to hate the Spotmatic stop down meter switch. The location could be better (e.g. Fuji has a button you sqeeze with your right hand; Yashica has a sliding switch at the bottom of the OTHER side of the prism/lens mount, where you have a choice of several means of attack)... plus the Spottie switch tends to get sticky when old...
The hardest to use camera I have is the National Graflex. The number of persnikity operations needed to reset mirror, advance film, arm shutter, set speed, set focus and set aperture is higher than I can recall with any other camera, and inevitably confusing.