stylistic:tone, structural:summarization, quality:correction
Perceived decline in quality

Critics' reviews of early Simpsons episodes praised the show for its sassy humor, wit, realism, and intelligence. However, in the late 1990s, around the airing of season 10, the tone and emphasis of the show began to change. Some critics started calling the show "tired". By 2000, some long-term fans had become disillusioned with the show, and pointed to its shift from character-driven plots to what they perceived as an overemphasis on zany antics. Jim Schembri of The Sydney Morning Herald attributed the decline in quality to an abandonment of character-driven storylines in favor of celebrity cameo appearances and references to popular culture. Schembri wrote in 2011: "The central tragedy of The Simpsons is that it has gone from commanding attention to merely being attention-seeking. It began by proving that cartoon characters don't have to be caricatures; they can be invested with real emotions. Now the show has in essence fermented into a limp parody of itself. Memorable story arcs have been sacrificed for the sake of celebrity walk-ons and punchline-hungry dialogue."

In 2010, the BBC noted "the common consensus is that The Simpsons ' golden era ended after season nine ", and Todd Leopold of CNN, in an article looking at its perceived decline, stated "for many fans... the glory days are long past." Similarly, Tyler Wilson of Coeur d'Alene Press has referred to seasons one to nine as the show's "golden age", and Ian Nathan of Empire described the show's classic era as being "say, the first ten seasons". Jon Heacock of LucidWorks stated that "for the first ten years, the show was consistently at the top of its game", with "so many moments, quotations, and references – both epic and obscure – that helped turn the Simpson family into the cultural icons that they remain to this day".

Mike Scully, who was showrunner during seasons nine through twelve, has been the subject of criticism. Chris Suellentrop of Slate wrote that "under Scully's tenure, The Simpsons became, well, a cartoon... Episodes that once would have ended with Homer and Marge bicycling into the sunset now end with Homer blowing a tranquilizer dart into Marge's neck. The show's still funny, but it hasn't been touching in years." When asked in 2007 how the series' longevity is sustained, Scully joked: "Lower your quality standards. Once you've done that you can go on forever."

Al Jean, who was showrunner during seasons thirteen through thirty-three, has also been the subject of criticism, with some arguing that the show has continued to decline in quality under his tenure. Former writers have complained that under Jean, the show is "on auto-pilot", "too sentimental", and the episodes are "just being cranked out". Some critics believe that the show has "entered a steady decline under Jean and is no longer really funny". John Ortved, author of The Simpsons: An Uncensored, Unauthorized History, characterized the Jean era as "toothless", and criticized what he perceived as the show's increase in social and political commentary. Jean responded: "Well, it's possible that we've declined. But honestly, I've been here the whole time and I do remember in season two people saying, 'It's gone downhill.' If we'd listened to that then we would have stopped after episode 13. I'm glad we didn't."

In 2004, cast member Harry Shearer criticized what he perceived as the show's declining quality: "I rate the last three seasons as among the worst, so season four looks very good to me now." Cast member Dan Castellaneta responded: "I don't agree,... I think Harry's issue is that the show isn't as grounded as it was in the first three or four seasons, that it's gotten crazy or a little more madcap. I think it organically changes to stay fresh." Also in 2004 author Douglas Coupland described claims of declining quality in the series as "hogwash", saying " The Simpsons hasn't fumbled the ball in fourteen years, it's hardly likely to fumble it now." In an April 2006 interview, Groening said: "I honestly don't see any end in sight. I think it's possible that the show will get too financially cumbersome... but right now, the show is creatively, I think, as good or better than it's ever been. The animation is incredibly detailed and imaginative, the stories do things that we haven't done before, so creatively there's no reason to quit."

In 2016, popular culture writer Anna Leszkiewicz suggested that even though The Simpsons still holds cultural relevance, "contemporary appeal" is only for the "first ten or so seasons", with recent episodes only garnering mainstream attention when a favorite character from the golden era is killed off, or when new information and shock twists are given for old characters. The series' ratings have also declined; while the first season enjoyed an average of 13.4 million viewing households per episode in the U.S., the twenty-first season had an average of 7.2 million viewers.

Alan Sepinwall and Matt Zoller Seitz argued in their 2016 book titled TV (The Book) that the peak of The Simpsons are "roughly seasons 3 –12", and that despite the decline, episodes from the later seasons such as " Eternal Moonshine of the Simpson Mind " and " Holidays of Future Passed " could be considered on par with the earlier classic episodes, further stating that "even if you want to call the show today a thin shadow of its former self, think about how mind-boggingly great its former self had to be for so-diminished a version to be watchable at all."

In 2020, Uproxx writer Josh Kurp stated that while he agrees with the sentiment that The Simpsons is not as good as it used to be, it is because "it was working at a level of comedy and characterization that no show ever has." He felt there were still many reasons to watch the series, as it was "still capable of quality television, and even the occasional new classic" and the fact that the show was willing to experiment, giving examples such as bringing on guest animators like Don Hertzfeldt and Sylvain Chomet to produce couch gags, and guest writers like Seth Rogen and Evan Goldberg, Pete Holmes and Megan Amram to write episodes. In the season 32 episode " I, Carumbus ", the show itself makes a nod to these concerns in its credits gag where the god Jupiter notes that "It definitely feels like they're wrapping it up... any day now."

In a 2021 interview with NME, Jean was quoted as saying, "To people who say The Simpsons isn't as good as it used to be, I would say I think the world isn't as good as it used to be. But we're declining at a slower rate."