It's evidence of the increased prestige of science fiction in the late sixties that this was assigned an A list director- Franklin Schaffner- for what looks a B film premise. An astronaut (able to traverse time as well as space) lands on a planet with a habitable atmosphere in the distant future, where the great apes are the dominant species-and speak English!
Humans are the mute, unreasoning beasts. Charlton Heston discovers an earth-like environment, but because his instruments are telling him that he is way over the other side of space, he doesn't draw the obvious conclusion... at least until the famous ending.
Schaffner gets more from his budget than just a major star. The visuals are fabulous, particularly the location shots in the Utah desert. There is a classy score. There are no noirish atmospherics. This is in bright, colourful Panavision, but the irregular, jagged constructions of the ape city give the film an unsettling, distorted look. Best of all are the ape costumes and make-up effects.
For an action film there is quite a lot of thematic content. It touches on the conflict between evolution and religious dogma. The schism between the gorillas and chimpanzees encourage reflection on contemporary American racial conflict. It is about the social and political realities of 1968, the year of revolution on campus, with prejudice, belligerence and superstition ascendent over reason.