Star Trek TOS
I had watched a lot of TNG, DS9 and Discovery, but I had never watched the original series.
Yesterday I saw it was on Netflix, started watching the first pilot (The Cage), and I absolutely loved it. It does have the cheeky acting, crappy costumes and obviously painted backgrounds... but holy crap, the story is good. Especially for a pilot, and especially for a TV show from 1964!