Citizen Kane
@9point6@lemmy.world has a comment below stating that some of these are examples where a piece of media did something new and innovative that was so compelling that many subsequent pieces of media copied it, and thus whatever it was that the piece of media did failed to impress later audiences. For them, it was just the new normal. So the work was very influential...but maybe no longer stands out.
I've often seen Citizen Kane cited as being the poster child for this.
https://en.wikipedia.org/wiki/Citizen_Kane
The film's narrative structure, cinematography and themes have influenced countless filmmakers and films worldwide, asserting its place as a cornerstone in the history of cinema
EDIT:
https://thecinemaholic.com/citizen-kane-innovations-flaws/
‘Citizen Kane’: The Innovations, the Flaws, and the Films that it Influenced
EDIT2: @marzhall@lemmy.world linked to the Seinfeld is Unfunny trope on TVTropes, and it has an entry for Citizen Kane:
Citizen Kane, oftentimes trumpeted as "The Greatest Movie of All Time," tends to inspire "what's the big deal?" responses from modern viewers, especially since Post Modern movies have become the norm and the cinematography has influenced so many other films. And everyone knows what the twist at the end is.