These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Acting for Two: Ronnie Claire Edwards played both Corabeth and her lookalike sister Orma Lee.
Bizarro Episode: The episode 'The Changeling' is about a poltergeist invading the Walton home. No other episode features any overt supernatural elements (though 'The Ghost Story' is ambiguous about a Ouija Board) and this is never mentioned again.
Signature Scene: An exterior shot of the house as everyone wishes each other a good night, ending with "Good night, John Boy."
Tear Jerker: The season 6 episode "Grandma Comes Home" combines this with Harsher in Hindsight: It's Grandma Walton's first episode back after Ellen Corby's stroke, but it also ends up being Grandpa's last because Will Geer died during the show's hiatus. The season 7 premiere "The Empty Nest" deals not only with the loss of Grandpa, but also Flossie Brimmer (whose actress had also died).
They Changed It, Now It Sucks: Several fans dislike Season 9, mainly because of the different actor for John-Boy and the episodes that focus on the sons fighting in the war. Also, by this point four of the original cast members had left.