LOTG can become tiresome because many of the episodes have the same plot. Giant captures one or more earthlings; the remaining earthlings rescue the captive. Zzzz.
THE CLONES stands out because of the interesting story penned by Oliver Crawford, who only contributed one episode to the series. When the curtain rises, Valerie and Barry are ALREADY captive (taken by giant scientist Bill Schallert, known for his role on PATTY DUKE and almost every other significant 60s show). They seem normal, but they begin to notice strange changes in their bodies and their behavior.
As the episode progresses, the real enemy is not the giant, but the various clones of the Spindrift crew. Confusion grows, because the clones have the same memories as the real earthlings. And finally, that stupid dog has something significant to do besides his usual routine of barking and/or running away.
We've all heard so much about cloning that it's hard to believe it was still new enough in 1969 to demand an explanation by one of the crew members. So it's a forward-looking plot from that perspective. It's also the only episode I can remember that actually points out that Dan is black, and makes it a crucial plot point. So three cheers for Oliver Crawford, for breaking the mold.
Oh, and while you were trying to count all the clones, did you notice that Betty is invisible in this episode?