Honestly? Stargate SG1. One of my favorite shows.

The whole theme of the first seven or so seasons was teching up and gathering allies to say "you're not my real dad/god" to the evil sufficiently advanced aliens.

But then having reached the end of that arc and wanting to keep the show going, they introduced some even more godly evil aliens who weren't just sufficiently advanced but were actual magic. I felt it deflated the point made in the whole first arc, that there ain't nobody better then you, to then trot out some evil canonically supernatural entities.

Arrested Development

The Simpsons

Amazon's The Rings of Power.

It should have been cancelled 8 episodes ago.

Stargate: SG-1 should have ended at season 8. They beat Anubis, all the conflicts were tied up, there's a nice scene where the crew is just relaxing at O'Neill's pond. And then they ordered another season. So they did the same thing that Xena did and said "Well we ran out of ancient dead religion gods, I guess Christianity is next except they still exist so we have to be kinda cagey about it" and just kept making the show.

The Office (US version). NBC should've put it out of its misery after Pam and Jim married if they had to hold on to airing it. But really it could've ended way earlier than that.

Archer.

Small show, but Eureka. Everything after the time traveling reset shouldn't have been made.

The Battlestar Galactica reboot should have ended after Season 2; 3 was meh and 4 was terrible.

Scrubs should have been done with season 7, saying good bye to JD. no weird season 8 with new side stories that all sucked!!

Oh and Family guy... when Seth left the writing and production of the show and only did voicing, the shows quality changed .. it's funny, but its no where near as on the nose funny as season 1 through 10.. now when they break the fourth wall for a brake away joke, it just feels... off.. peter is not ironically funny anymore.. the meg jokes got stale and honestly cruel to where it was not Soo funny anymore.. Lois used to be a great loving mother, even to meg, then became just cold and unrelatable to me... Stewie was funnier as a world domination deviant before they completey changed his character around.., Brian used to be more relatable and then just got pretentious and misogynistic that really wasn't ironically funny anymore.. Chris is maybe the one character who has barely changed from the early seasons... idk it's just not that funny any more to me..

The last season of Scrubs. They basically switched out the main character. Should have been a different show.

Spongebob had an astounding three season run. I could probably even go to bat for a few of the season four episodes.

But thirteen seasons and counting? Other than handsome Squidward, I can't think of a single joke/scene that people love from an episode post-movie.

The canonical answer is "Happy Days".

For me, Lost.

Writers introduced way too many mysteries that they didn't resolve. ABC should have given them less episodes so they were forced to tie up loose ends faster.

The expanse (the novels). Time jumps in sci-fi are hard to do right. The show had the good sense to end it before the time jump, but they still had to put in admiral Duterte and MCR II (Laconia) in the final season with little to no follow-up because that was in the books

I remember watching a couple of episodes of Under The Dome and then getting bored of the concept and bailing on it. I forgot about the show for a couple of years and then saw something advertising a third season and I was like "How are they still under that fucking dome?!"

House of Cards

NCIS

The office should have ended when Mike left.