The first thing you need to know is that you should not watch this movie without first having seen Unbreakable and Split. Glass brings together characters and events from those two movies so it really won't make any sense if you haven't seen those two. If you have seen one or both of those and didn't like them, well, you can probably skip this one for the same reason - it's a continuation of the two.
In Glass, the characters played by Bruce Willis, Samuel L. Jackson, and James McAvoy in the previous two movies are brought together by a psychiatrist, played by Sarah Paulson. What ensues is a battle of wills - will the men be convinced that their delusions of grandeur are just that - delusions? I don't want to share much more for risk of giving the story away, but suffice it to say the movie was excellent.
McAvoy continues showing off his acting chops with his character - honestly, that alone makes the movie worth seeing for me. The story held me in its grip the entire time and, per usual, director M. Night Shyamalan managed to surprise me as well. The end seemed to be a set-up for a fourth movie and I sure hope that comes to fruition - I would definitely head to the theater again to watch another installment of this fascinating tale!
If you haven't seen the first two yet but this movie intrigues you - go binge on Unbreakable, then Split (that order, please) then head out to your local theater to catch this one! It's worth it!