Indiana Jones and the Kingdom of the Crystal Skull is often viewed as the black sheep of the franchise due to its departure from the familiar formula. The change in setting, introduction of new characters, and heavy reliance on computer-generated effects (CGI) instead of real location shooting deviated from what fans cherished in the original Indiana Jones Trilogy. However, in a similar fashion to how the first three films drew inspiration from 1930s adventure serials, the fourth Indiana Jones film embraced B-movies from a different era.
Source：https://www.cbr.com/indiana-jones-kingdom-of-the-crystal-skull-50s-b-movie/
