In the best tradition of modern myth-makers, Farmer borrows elements from world culture for his setting. There are bards as in Celtic legends, as well as the shamanism of Native American lore. Hadon is the typical small-town king in the making, a man from humble beginnings who shows his prowess with both fighting skills and his leadership ability. At first naïve about the wider world, Hadon becomes more and more experienced as he fights in relatively controlled games before his jungle battles with the stakes rising the further he goes.
All of this is fine entertainment, but it really is just a vivid comic book. By comparison, even in the cartoonish Lord Grandrith books (Farmer's name for the "real" Tarzan), we see inside the character as much of his story is told in the first person. So we hear what Grandrith thinks and desires and feels even if his extended penis is typically protruding unashamedly for all to see. Hadon doesn't have this affliction, and we rarely know anything going on inside him. He moves from scene to scene as an archetypal stock character. There's nothing wrong with that, but there is a reason Hadon never found a place in popular culture alongside characters like Conan, Luke Skywalker, or Tarzan and Doc Savage. There's simply nothing to distinguish him.
Again, if you're looking for a fast-paced action-adventure yarn in the pulp tradition, Hadon of Ancient Opar is light reading. It's just lighter than all the supplementary material would lead you to expect.