If you have read much science fiction you at least know of John Carter and Barsoom (AKA Mars).
The stories are not really science fiction as we would think of it today, but sword and planet. I find them interesting partly because they show how far science fiction has come.
While the books do not have the deepest characters what they do have (particularly the first couple) is a level of world building I hope I will one day approach.
The stories have people that are often brutal, different in ways its hard to imagine but who you feel sorry for. They invoke a feeling of wonder, of meeting people you can admire, or hate but will never really understand.
Honestly its hard to quantify how Burroughs did it, but it works and it does so with seaming effortlessness.
The main character, John Carter, also does something I wish more characters did in fish out of water type situations, he accepts the people he finds as they are and acts according to their value system when he has to. If this means killing that is what it means