The first two Godfather movies have earned their place among the greatest films ever made, and sadly, The Godfather Part III could not live up to their legacy. After making movie history when The Godfather and The Godfather Part II both won Academy Awards for Best Picture, when the franchise returned after 16 years in 1990, it did not stack up against the reputation of its predecessors. With convoluted plotlines, miscast characters, and a rushed script, The Godfather Part III had many issues that meant it was forever doomed to be considered the weakest entry in the series.

https://screenrant.com/godfather-3-worse-other-movies-reasons/