A complete letdown.
I've seen all three of the trilogy, but only recently watched Glass when it came on Netflix. I'd already caught a couple of reviews and almost didn't want to watch it to avoid the disappointment that seemed likely.
I had problems with the other movies. Minor things that didn't completely ruin the films, but things that stuck in my mind even years later. For example, in Unbreakable, there is this scene where the Bruce Willis character is figuring out his powers and he bench presses 350 pounds. Yes, for most normal people 350 pounds is a significant amount of weight. But the world record is something like 1,400 pound and there are hundreds of athletes that can easily lift that much. To me, it doesn't qualify as "superhuman" or "super strength".
Anyway, Glass has too many plot holes and too many inconsistencies to be enjoyable. McAvoy is great: he shines in his role. Jackson and Willis do what they can with their limited material. Jackson has to appear comatose or drug-addled in many of his scenes. Willis isn't really given much to do and is put in the unenviable position of having to sell a story that is completely unbelievable (the shrink in the movie is trying to gaslight him and McAvoy that they aren't superhuman. Given that at the time of the movie, Willis has been doing the secret superhero act for the previous 20 years, it seems unlikely he'd chase that rabbit down the hole).
In the end, McAvoy is killed by a bullet (whereas he survives being shot in Split) and Willis is overpowered by a couple of normal human cops and drowned in a puddle (who then, inexplicably, then proceed to try to give him CPR).
It is a movie that not just insults but also assaults the viewer's intelligence at multiple points. Whatever touch Sayamalan had was lost years ago and this movie just confirms his incompetence as a storyteller.