I have only vague memories of this show, in it's various incarnations. What I do remember is the great animation (for Filmation, anyway) and the entertaining stories. Despite the prohibitions against violence, Filmation was still able to keep the adventures exciting. The use of rotoscoping, where animation is drawn over film of live action, gave it a more fluid movement. The only real problem was the use of stock footage, to keep the costs down. It tended to make the episodes somewhat repetitive. I do remember that there were many stories about lost civilizations, much like Opar, from the novels. It was a definite change of pace from the typical Saturday-morning fare of the time.
It's too bad that Filmation's work is unavailable in the US (except for recent releases of Fat Albert). They produced many great shows, although many were licensed products and not actually owned by the studio. I would love to have DVD's of Tarzan, Flash Gordon, Zorro, Shazam, Isis, Space Sentinels, The Groovie Goolies, and other shows.