I think people we're expecting another marvel movie. However 3 movie spoilers!
Unbreakable 2000 gave us the human superhero that we still try to eliminate to this day in film/series (before anyone else) and the friend then foe villain. An abnormally intelligent and fast but psychically weak villain. The Hero can't swim easily because of the density of his bones.
Split 2016 gave us a manufactured by chance (influenced by unbreakable events years later) psychological powerful villain taken down by a girl with a similar broken mind. Mr Glass is referenced at the end of that movie.
Glass 2019 gave us the secret organisation that wants to hide that people like this exist in the world good or bad and tries to (and fails) to convince that this superpower complex is all in their heads. This brings together the 3 Every single main of previous movies... Spoiler again.
Dies. All by outside but predicted influence some more impressive than others. Then the mother of Mr Glass, the son of Unbreakable & the girl from split share the video proving that amazing people really do exist and breaks the foil of the supernatural complex to the whole world. It was a good ending but also allowed for further movies with different actors, skills and so on. I can see why people wouldn't like it but to me it followed what you'd put into a 'realistic, natural' super-powered universe. It also was a reminder that you could be so weak you could break in some ways like Mr Glass but that doesn't mean you don't have another strength. Uplifting actually.