From what I remember of the trailers, the trailers don't do the film justice. It's a pretty good movie, but the series of twists toward the end are unconventional and is likely one of the primary reasons a lot of viewers & critics were thrown off. That, and a lot of people just don't like Shyamalan's films.
I think the best movie in the trilogy is Split, with Glass coming in second, and Unbreakable third.