I first read this back in 1989. It's a direct sequel to "Tarzan the Untamed," where Edgar Rice Burroughs decided to kill off Jane so Tarzan could have more and different love interests, but Burroughs' wife put her foot down and wouldn't have it, so at the end of that novel, he reveals that Jane lived after all, and it was just a Nazi plot to make Tarzan think Jane was dead. It never really made sense, since Jane dying only resulted in Tarzan entering the war and killing tons of Nazis in revenge, and there was no real purpose in making it appear she was dead. Anyway, ERB had to appease his wife, so she lives.
And thus, in Tarzan the Terrible, Tarzan goes in search of his kidnapped Jane. I enjoy this novel a lot. It has dinosaurs and a lost culture. The dinosaur, a gryf, is a carnivorous descendant of the Triceratops, and it's wonderful to behold. The lost culture of Pithecanthropus descendants is marvelously detailed. The world-building here is phenomenal. You have multiple races of Pithecanthropus, and the dominant race is split by factions, primarily between the religious caste and the warrior caste, but also by lesser kings of various tribes. It's a situation rife with tension, and Tarzan makes a wonderful catalyst to burst that tension into tangible (and violent) change.
Tarzan, of course, is Tarzan of the Apes. I think most people have an idea of who Tarzan is without me having to say much. He's one of the best known literary characters of all time, sharing company with the likes of Sherlock Holmes, Dracula, and Frankenstein, a character that people know even if they've never seen the character in a movie or read the novels. Yes, some would argue Tarzan displays the problematic White-Savior trope, and there are a lot of racial/cultural objections one could make toward the character and/or author, but I am not here to be on a soapbox either for or against that type of reading. For me, I find the adventures to be thrilling escapism.
I also acknowledge that while I do enjoy the stories, they are not particularly well-written. Not only is ERB's writing formulaic from book to book, its formula is repetitive even within the novels. It's always progress for the character, setback, progress, setback, progress, setback. Much of the progress is hinged on chance and coincidence. Much of the setbacks involve the character getting captured repeatedly. I don't recommend reading ERB novels one after the other. Let some time pass between his novels, lest the formula really grow grating. That said, I've never had much of a problem with formulaic writing: I'm a huge fan of Perry Mason and Stephanie Plum. As I have said before of these, I know what I am getting when I pick up one of their novels, and when I pick up their novels, it's because I want what they are offering. They deliver exactly that.
Jane was interesting in this novel. She basically rescued herself, made weapons, a home, defended herself from a German, found food, and pretty much only re-united with Tarzan via a chance meeting as Tarzan was escaping his captors and happened on Jane's hut that she built in the lost valley. I rather liked that she basically saved herself and was able to live in the wilds on her own.
Also, I liked that the book included Korak the Killer, the son of Tarzan and Jane, although his identity is not specified until the end, there aren't a lot of people of his description wandering through central Africa. His adventures were short herein and he never really was dealt the setback of being captured, like everyone else in the story.
Tarzan uses religion against his enemies, and, at the same time, re-ignites religion in his friends by posing as the son of their god and instilling new values into their violent, people-sacrificing practicies. He makes friends with the noble and kind, and enemies of the cowardly and cruel. Tarzan teaches the white, fur-less Pithecanthropus people to be friends with the black, furry Pithecanthropus people. By the end of the novel, Tarzan frees all the slaves and forbids human (well, Pithecanthropus) sacrifice. He eliminates the extant priesthood, and orders that from now on, the women will tend to the temples.
While not a literary masterpiece by any stretch of the imagination, I love this novel for its adventure, the dinosaurs, the lost world of Pithecanthropus peoples, and Jane's depiction as capable and heroic in her own right. This remains a favorite of mine among the 24 Tarzan novels ERB wrote. Yes, it is formulaic, but when I wanted a rollicking adventure with a superheroic protagonist, this fit the bill perfectly.