I need to rewatch the original King Kong to see if it holds up on its own merits or if it's more of a classic because of what a milestone it is.

The original Godzilla is a legitimately great movie. Very eerie and foreboding. In fact, my only knock against it is its undermined by the goofiness of the guy in the Godzilla suit. With the wacky tone of all the subsequent Godzilla movies (that I've seen) the rubber suits fit in better.

There are plenty of other giant monster movies that are fun, or with amazing effects, but none are even close to my top whatever list. Just never seem to get the story/characters right for a cohesive whole.