I love sci fi movies. Maybe even especially the bad ones, since they're the ones I grew up with.
There's two kinds of "bad". There's the bad that's just so cheezy it's entertaining for just the badness factor, like Plan 9 from Outer Space,
widely regarded as the worst movie ever made. Anything with a guy in a rubber suit where you can see the zippers qualifies. Extra points for scenes
where the boom mic swings down into the shot.
Then there's the "boring bad". Not bad enough to qualify as entertainingly bad, and no redeeming value at all.
If I had to pick ONE, I might choose This Island Earth. At least today. Another one that comes to
mind as a favorite bad one is The Brain Eaters.
But I could probably list close to a hundred from the late 50s through mid 60s era, many made to run as double features at drive-ins.