I remember one day hearing my father downstairs laughing his ass off. Went down to see what was so funny to find he had just discovered Mystery Science Theater 3000, and was losing it watching The Giant Gila Monster. I sat down to watch. I didn’t really get it then, but I’ve been a fan ever since.
I use the movie to introduce people to the show. It sets up the whole universe without tons of in-jokes that newbies won’t understand. And “This Island Earth” is a weird combo of being a decent enough movie while still being infinitely mockable.