'Conquest of the Planet of the Apes' is the weakest of the first four films. It's watchable, still.
It shares similarities to 'Rise of the Planet of the Apes' from the rebooted 2010s series, though it isn't quite as entertaining or convincing. Serviceable it is, however. Roddy McDowall stays in the franchise, but as a different character in Caesar. McDowall is the clear standout from the cast, the rest of whom are solid if forgettable.
I found the real world parallels a bit too forced in this one, while the long speeches near the end feel over the top. For the early 1970s, though, the look of the film remains pleasant - I do like watching these films, after all this is - in my opinion - still a passable flick; if indeed the weakest so far.