Off the bat, acting was actually quite strong. That's the only saving grace in the movie. All the leads were skilled and played their parts well. The concept of the movie was unique, and I like how Shyamalan didn't turn this cheesy or put in some unnecessary love interest like so many directors are want to do.
But a movie with a poor script and barely convincing direction is not going to succeed. And that is where this movie fails compared to the two prequels. The movie was unconvincing and to put it mildly, boring. There was no suspense or plot twists.
As for the last 'plot twist', let's be honest, that's practically Movie Standard Plot Twist. I won't be saying what it is, obviously, but it was exactly what I expected. Cliché and annoying.
Hassan Minhaj in one of his stand up works has described Shyamalan movies as having a big build up with little payoff, and he is spot on.
It is an average to poor movie. I'm not sure it's even worth the watch. Go only if you get highly discounted tickets and free popcorn.