Read an oral history of Conan O'Brien's The Simpsons Marge vs. the Monorail episode
https://www.vice.com/en/article/akdzx5/an-oral-history-of-marge-vs-the-monorail-the-simpsons
The January 1993 episode changed The Simpsons. "By season four," says Sean Cole. "The Simpsons had entered what many now consider to be its golden age (although, at the time there were already suggestions that it was losing its way). 'Marge vs. the Monorail' (S4, E12), with its grand scale, silly asides and abundance of absurdist humour, represented a stark departure from the show’s established formula. While initial reactions were mixed, it’s now widely regarded as one of The Simpsons’ best-ever episodes."