Caught it over the weekend and I definitely liked it more than the critics did but I do agree that the third act gets very weak in parts.
The first 20 minutes are awesome. It's definitely the movie I thought we were going to get and what the trailers had seemed to promise. The first interaction between David and the Horde was awesome and seeing where all of the characters were after Split was great. Once they move into the mental facility it got pretty interesting and I found myself enjoying it more than I thought I would.
McAvoy is the standout here and it's a shame the Academy will never recognize his performance in this and Split. This guy is going to win an Oscar very soon. Bruce Willis is good but to be fair the character was never a showy type of role anyways. Samuel L Jackson is great but unfortunately doesn't get much acting to do until the 3rd act.
The supporting cast is okay. Anya Taylor Joy doesn't get a ton to do until the end either. I like Sarah Paulson but she does a lot of monologuing in the movie. Spencer Treat Clark starts off solid and in the 3rd act he just felt like he was in a different movie. The gal who plays Elijah's mother was not good at all and her old lady make up was super distracting. David's son and Elijah's mom in particular are in two of the worst scenes of the movie where they try to give an exposition dump and relate it to comic books.
The reveal at the end did work for me though and I found what M. Night did for the universe quite interesting. It felt like an ending but also an easy way to open up the door for a future story in this world but I think he should move on to new stories now.
Spoiler
As for those two scenes...
The scene where our three supporting characters meet in Sarah Paulson's office as the breakout happens turns into some Happening level style bad dialogue. Elijah's Mom likens the breakout to a limited edition and hearing her try and talk about comics just seemed so strange. She talks about it like nobody gets that Elijah's plan is to have Dunn and the Horde face off in front of the world (cameras) and it seems as if M. Night didn't think his audience was paying attention to the movie.
The second scene is once The Horde is about to leap on Dunn and Dunn's son runs in the middle of the action and gives the reveal that The Horde's father was on the same train as David from Unbreakable and that crash not only created David but also created the Horde. His delivery of the reveal is so bad and I felt the cringe real hard in that scene.