It depends on when he was chosen (or rather accepted since Cubby Broccoli always coveted him for the role). If Moore took over instead of Lazenby with "On Her Majesty's Secret Service", that film (which is widely regarded already by Bond fans as one of the best ever Bonds) would probably be regarded up there with Casino Royale as the best. Diana Rigg might not get hired as Tracy (they hired her to give Lazenby an experienced name actress to work with) and an unknown might have the part of Mrs. Bond. "Diamonds are Forever" (sans Connery) is probably a MUCH, MUCH better film since it would be continuation of OHMSS instead of Eon trying to forget that since there was another change in actors. Everything else is pretty much the same, except maybe Moore does call it quits with "For Your Eyes Only" (when he wanted to quit) or "Octopussy" and either Brosnan or Dalton (or Sam Neil, who impressed Cubby's kids back in the 80s auditions) take over for "A View to a Kill".