Son of Godzilla (1967)
What it's really about: The Godzilla Family: they're just like us.
When Godzilla finally shows up: 30 minutes in, when Manilla, her newborn, has his butt kicked by some giant praying mantis
Human plot: 3 - Some scientists go to Monster Island to perform weather experiments, which seems like the last place anyone would want to run weather experiments.
Monster action: 5 - Lots of stuff with Manilla is played for laughs, but Godzilla kicking the crap out of giant praying mantis ("Kamacuras") and a giant spider ("Kumonga") isn't horrible.
Camp factor: 8 - Tries to make monster parenting relatable by anthropomorphizing Manilla's behavior. Unless your kid plays jump-rope with his or her tail, you won't relate.
Mothra vs. Godzilla (1964)
What it's really about: Don't mess with cultures you don't understand.
When Godzilla finally shows up: 33 minutes in, emerging from the ground at a beach. Someone buried Godzilla?
Human plot: 3 - Some journalists and a scientist find a Mothra egg, but a greedy businessman steals it away, pissing off a pair of tiny singing fairies and Mothra. This is why Bernie Sanders hates the 1%.
Monster action: 4 - How does a giant moth fight a giant lizard? With a lot of wind attacks and a lot of confusing close-ups. It's fine, but Mothra fights always have trouble distinguishing themselves.
Camp factor: 7 - Toho fell in love with Mothra's plot-convenient life cycle and singing six-inch tall fairy twins. Later in Godzilla's lifetime, the creature even gets her own series (twice!).