Aliens spent its first hour having Ripley battle a single xenomoprh on a spaceship before introducing the queen and hive, and you can understand why Beneath the Planet of the Apes (1970) goes wrong.
The first sequel to the seminal Planet of the Apes, Beneath the Planet of the Apes is equal parts expansion of the story and characters introduced in its predecessor and rehash. The new elements presented here are quite good and help flesh out the world and mythology of the series before arriving at a conclusion of startling finality and pessimism. The regurgitated elements find a new, less interesting main character going through the same beats Charlton Heston did, and the second time around is not as effective.
Beneath introduces a new astronaut, Brent (James Franciscus), who arrives on the planet looking for Taylor (Heston), who has disappeared into the Forbidden Zone. For the first forty minutes, Brent goes through the same paces Taylor did: encountering the ape society, meeting Zira (Kim Hunter) and Cornelius (now played by David Watson, making this the only of the original Apes movies to not feature Roddy McDowell), and escapes into the Forbidden Zone with a mute human, Nova (Linda Harrison), who was Taylor's girlfriend in the first movie. His discovery that he's on Earth occurs on a subway platform.
This first half of the movie plays like a condensed redo of the first movie. It even opens with stock footage showing the Statue of Liberty climax, and stock footage is never a good way to open any movie that aspires to be epic or convincing; it always comes off as cheap and jarring. The film also glosses over a few questions raised by the end of the last movie. When the original ended, Zaius declared Zira and Cornelius were going to be charged for heresy, and yet that's never mentioned in Beneath, and Zaius is comparably friendlier toward the pair of human sympathizers.
Most disappointing of all, the sequel limits Zira and Cornelius to only a handful of inconsequential scenes; they could have been easily written out of the film for all they contribute. Previously, their fates became entwined with Taylor's, and the growing trust and friendship among the three was one of the movie's strengths. Here, they give Brent some clothes, and Zira later helps him escape. It's a hollow echo of the same storyline and has none of the same impact.
The one wrinkle in this sequence is the expansion of the caste system among the apes - with the elite orangutans ruling as political and religious figures, the militant gorillas as police and soldiers, and the intellectual chimpanzees as the low rung on the totem poll. All apes are equal, we were told at Taylor's trial, but ape society is clearly segmented and opposition is suppressed. When the gorilla army marches out of the city, several chimpanzees stage a protest, holding signs and chanting for peace, and the gorillas respond by arresting them.
Beneath also lays bare the hypocrisy of both apes and the mutants; both sides believe, in the words of the film, they are "God's chosen." The mutants insist the bomb is a weapon of peace, that they do not kill anyone but instead make their enemies kill each other (by subverting their free will). They also torture people, bombarding their minds with pain while sanctimoniously insisting they have superior brains. Meanwhile, the apes launch a campaign of conquest and call it a "holy war" with themselves as "God's chosen servants." Gorilla general Ursus (James Gregory) gives a speech to the assembled apes, calling for the extermination and enslavement of humans. "The only thing that counts in the end is power, pure, merciless force," he declares. The apes believe they have a manifest destiny, which justifies warfare and slaughter.
In the end, when the apes attack the mutants, the mutant plan is to set off the bomb, which would destroy the planet, and Taylor tells Brent, "We should let them all die." In actuality, Taylor, dying from a gunshot wound, is the one who ends it all, activating the bomb with his dying breath. By this point, he's seen Nova murdered, Brent mercilessly gunned down, and his own plea for help from Dr. Zaius scornfully rejected. "You bloody bastard" are his final words. In an instant, Earth is incinerated; everyone dies. Two warring sides, both convinced of their righteousness and blind to the truth, destroy everything.
Ultimately, a script rewrite could have solved a lot of the film's problems. Taylor should have been the main character, the person we follow the whole time, and we should have started with his encounters with the mutants. Reportedly, Heston wasn't interested and only agreed to appear in a couple of scenes. In that case, the torch should have been passed to Zira and Cornelius; they should have been the protagonists, and the movie could have focused on their efforts to stop the war and find Taylor. That would eliminated having a relatable human at the center of the story, but I think it could have worked. It would have been the kind of bold decision the first half of the movie really needs.
Beneath the Planet of the Apes is an appropriate title. Not only does it accurately convey where the story takes place, it indicates this sequel is a step down in quality from the original.