I really like Diamonds Are Forever. No, it's not a great Bond film, but it is so straight-up bizarre I find it compulsively watchable. One thing the movie has going for it is some glimpses of Las Vegas as it used to be, before being remodeled by corporations as a family vacation spot. (Sammy Davis Jr. even acted in a scene that was cut from the film). The ending is incredibly weak, though (especially Blofeld's exit) and I can't figure out the tape-switching plot, either.
Regarding the lunar chase scene - I think it's supposed to imply that the 1969 moon landing was faked by NASA with support from Howard Hug-- er, Willard Whyte.
Charles Gray wasn't just a memorable Blofeld - he also played The Criminoligist in The Rocky Horror Picture Show (you know, the stuffy professor who teaches the dance steps for "The Time Warp."). Cult film fans will remember him forever.