The transition (a missing link, if you will...) from the Gothic Monster to the Atomic Age. That intro is so very Kirby-esque.
The plotting drags on with the Creature continually harrying and fleeing from the expedition, but there's so much to dig in here! Very fascinated by the film's colonial ideal of the Amazon as this untouched, virgin frontier "as it was in the Devonian" when humans have been living there for generations. Someday I will write about literature's sexual fascination with the fish-person... (sailor stories about siren-seductresses, selkie bridegrooms, the Deep Ones and Lovecraft's genealogical insecurities)