Movie trilogies have an incredible challenge when it comes to sticking the landing, but some movies pull it off exceptionally well. The last movie in a trilogy not only has the particular challenge of being a good film in its own right but also has to pay off storylines and character arcs from two other stories entirely. It is incredibly difficult to maintain consistency in quality across three separate movies because the stakes get higher each time due to heightened audience expectations. There are countless examples where the first movie, or even the second, is considered to be a masterpiece, but the finale simply lets the entire story down.

https://screenrant.com/movie-trilogies-peaked-with-third-final-movie/