This first sequel to the '68 science fiction hit has all the markings of something rushed into production. There was no time to craft a story which explores the truly interesting possibilities of astronaut Taylor's continuing odyssey on a future world turned upside down. The story could have and should have concentrated on the evolving struggle between the ruling class of apes and the backward humans. Instead, the filmmakers created a new threat for this film, a secret society of human mutants living underground. They show up in the 2nd half of this feature and, in prolonged scenes, show off their telepathic powers in torturing the heroes. The heroes, in this case, are another astronaut (Franciscus) who followed Taylor's trajectory to this other planet and Taylor himself (Heston, reprising his role briefly). Wow, what an original concept - another astronaut, who, in an accelerated version of the first film's events, also finds Ape City, encounters two sympathetic chimps, gets captured and escapes. Are we watching some kind of a repeat?
The quick pace of this picture is probably its best aspect; this stresses action. However, the pace is so fast that some crucial points in geography are sacrificed: getting to the Forbidden Zone from Ape City is just a short walk in a tunnel for some, while others have to trudge for days overhead. In a slight nod to the satirical aspects of the original film, we do get to see religion being mocked (the original satirized the social & political anchors of a community). But, it's not a very subtle jab. The mutants profess to be more intelligent than either the heroes or the apes, which they seem to prove with their advanced mind powers, but they spend most of their time worshiping a nuclear bomb, chanting silly songs - they really picked a strange form of idolatry, but maybe they're simply crazed. This movie throws together a lot of science fiction concepts but the resulting brew is rather bland. It's a decent action piece, not much more.
Franciscus shows he is no Heston; he overacts in most of his scenes, as if he had no clue on how to depict a man realizing where he's actually landed, but then again, he wasn't the skipper on this 2nd ship (the lead officer dies soon after they crash-land); we're not watching a leader but a follower try to carry the picture. I was struck by how Heston towered over him in their brutal fight scene. McDowall is also missing; his role of Cornelius is played by actor Watson. Evans & Gregory are pretty good as the ape leaders but whoever stuck them in ape suits for the sauna scene should have thought about it a few more minutes. This movie ends everything on a grotesquely conclusive note, but they managed to find a way to continue the story in 'Escape From the Planet of the Apes.'