The Simpsons has been named by Time as the greatest television series of the 20th century.
The 20th century ended in 1999. The last Simpsons episode from the 20th century was season 11 episode 9. You can see it was already in decline by then. The vast majority of the episodes were released in the 21st century. We’re a quarter of the way to the 22nd century and they’re still releasing them. But, it hasn’t been good since the last century even if Homer’s probably saying “it’s just a little slimy, it’s still good, it’s still good!” (S7E5, 1995)
From the Wikipedia page:
The 20th century ended in 1999. The last Simpsons episode from the 20th century was season 11 episode 9. You can see it was already in decline by then. The vast majority of the episodes were released in the 21st century. We’re a quarter of the way to the 22nd century and they’re still releasing them. But, it hasn’t been good since the last century even if Homer’s probably saying “it’s just a little slimy, it’s still good, it’s still good!” (S7E5, 1995)