Difficult to watch this without thinking of all the films that followed in its wake. Apocalypse Now most obv, although I think Herzog's film is much finer (and more compact), sticking close to its warrior-prophet from beginning to end. But Aguirre's influence might even be felt in things like Jackson's Lord of the Rings, where the Fellowship is being chased by orcs down the River Anduin.
None of these successors can quite capture the sense of precariousness in Herzog's film. The images he managed to get show quite clearly the reckless nature of the shoot – horses going crazy on floating rafts, men flipped upside down by jungle booby-traps. Like his hero, Herzog is a little touched by the that sense of capturing greatness at whatever cost. Unlike his hero, he knows when to stop... just.
The other unexpected element is the frequent sense of the bizarre: the almost Monty Pythonesque deaths of some of the minions, the exaggerated overacting of Klaus Kinski in the title role, that final circling image of Aguirre pacing the raft overrun by monkeys, muttering about the fame and power he will wield. There is a fine line being navigated between pathos and bathos, which is crucial to Herzog's theme of the delusions of imperialism. It is that sense of detachment, the silent observation of this preposterous treasure hunt's inevitable unravelling, which is the film's greatest achievement.