Star Wars: The Empire Strikes Back also comes to mind.
Though famous for "The greatest plot twist in the history of cinema", this so-called strength has forced people to unironically argue that new audiences need to watch the franchise out of sequence in order to properly enjoy it. By itself, that's a massive red flag, unintentionally highlighting the underlying problems in the ending. Whatever power that moment once had, it's long since been diminished by 25 years of extra content (the the writers/rights holders have always insisted we watch in order) and entire generations using it as a meme. Instead of being an otherwise powerful revelation, we are treated to information we already knew through some of the worst acting in Mark Hamill's entire career.
It doesn't stand on its own merits anymore, and thanks to the content of the Clone Wars and Rebels deflating most of the movie's worldbuilding, the non-ending renders Empire as actually the weakest installment in the Skywalker Saga. Strangely, the same cannot be said for the other movies. Revenge of the Sith, A New Hope, Rogue One, Return of the Jedi, even Solo are improved by subsequent movies/shows/games contextualizing their events on screen. Empire is alone in its suffering and again, that's probably due to its over-reliance on a plot twist instead of building up to a satisfying conclusion. With everyone faffing around through the middle, it was clearly telegraphed that having an actual ending was an afterthought.
Worse, when it brought the lazy storytelling convention of "To Be Continued" to the big screen, a number of franchises were misguided enough to follow suit, damaging the structure of their own trilogies in the process. There's a good reason almost no one argues that The Matrix Reloaded had a tight narrative with a satisfying conclusion. No, by foisting the burden of a proper ending to the third installment of a trilogy, the writers were given leeway for unnecessary bloat and allowed them to write themselves into a corner. If Empire can get extra points for raising expectations of a sequel, it sure as Hell loses points for this.
It is actually frustrating that neither the Empire, Rebels or main characters are closer to reaching their goals by the time the credits roll. The only one who actually managed to push the story forward was Boba. Unsurprisingly, that's what sets the stage for Return of the Jedi.
