Indiana Jones and the Kingdom of the Crystal Skull is widely regarded as the weak point in the franchise.

Source: https://www.cbr.com/star-wars-easter-eggs-indiana-jones/

Indiana Jones and the Kingdom of the Crystal Skull was delayed so long, the press surrounding the fourth entry constantly jabbed fun at Ford's age.

Source: https://screenrant.com/indiana-jones-5-harrison-ford-age-disney-record-break/

Kingdom of the Crystal Skull, especially as the film is one of the funniest entries in the franchise--whether intentionally or not.

Source: https://www.cbr.com/funniest-indiana-jones-movie-quotes/

"Last Crusade" is definitely the most broadly comedic of the Indiana Jones movies, but worse than the autopilot Spielberg of "Crystal Skull"?

Source: https://www.slashfilm.com/1175972/quentin-tarantinos-favorite-indiana-jones-film-is-the-one-steven-spielberg-likes-the-least/

Later, it's revealed that their son Mutt, who was played by Shia LaBeouf in Indiana Jones and the Kingdom of the Crystal Skull, died in the Vietnam War after enlisting.

Source: https://comicbook.com/movies/news/indiana-jones-and-the-dial-of-destiny-does-karen-allen-return-as-marion-ravenwood-spoilers-cameo/

Meanwhile, Stan, Kyle, and Kenny watch Indiana Jones and the Kingdom of the Crystal Skull and feel that the filmmakers have ruined the iconic character.

Source: https://collider.com/most-controversial-south-park-episodes-ranked/

Watch the Trailer for 'Indiana Jones and the Kingdom of the Crystal Skull'

Source: https://ksenam.com/ixp/295/p/indiana-jones-kingdom-of-the-crystal-skull/

What makes the new "Indiana Jones" and "Top Gun: Maverick" work surprisingly well is that they are not concerned with teasing a future for their franchises (unlike "Kingdom of the Crystal Skull").

Source: https://www.slashfilm.com/1326457/indiana-jones-and-the-dial-of-destiny-shares-an-ending-with-top-gun-maverick/