"Conquest Of..." seems to be maligned as one of the weakest in the Planet Of The Apes series, but actually after the almost rom-com style of "Escape From..." this film is a welcome return to the action adventure and confrontational nature- and, importantly, lots of apes- that were seen in the first two films.
It's another prequel, which picks up from "Escape From..." the story about how apes took over the planet. You should watch all the Apes films in order, otherwise they'll make very limited sense. It's set in 1991, which in 1972 probably seemed a long way in the future. In parts it's very much a film about 1972- the racism theme is handled with no subtlety at all, and the background science fiction elements, such as the technology being used in the civilisation, isn't really an attempt at science fiction at all- at one point when a filing clerk has to urgently check a record, we see him grabbing a Filofax style book and flicking through it to the right page. Didn't they think there might have been a computer or two by 1991?
The make-up is stunning and there are excellent performances from, among others, Roddy McDowall and Ricardo Montalban.
However the lack of budget begins to show in places. Almost the entire film seems to be set in one large modernist shopping plaza, and the same pieces of scenery crop up repeatedly through the film.
Two endings exist for this film- an original and much darker ending, and the eventual cinema ending which is very much softer. Only one ending appears on this DVD, and that's the "soft" ending, which very much looks like an afterthought to the rest of the movie. There's a Blu-Ray edition of this film which also includes the original ending, so big Apes fans should save their money for that.