As a movie, it's okay. There's a lot of plot holes though and it's very easy to see how cliche the story and ending is. In terms of how they dramatized and slandered a very real condition (Dissociative Identity Disorder, DID), it's extremely upsetting.
M. Night Shyamalan cherrypicked real facts to make the movie seem researched and credible, when in reality it's a grossly exaggerated and harmful film. Unknowledgeable and ignorant people see this movie and act like it's 100% factual and believe that people with DID need to be feared.
I understand that it's just a film, but pop culture affects everyone even in subconscious ways and this movie will only spread more fear and ableism in a society where it already thrives. Directors who thrive off such blatant disrespect should not be celebrated in mainstream media. People should be able to just live without being demonized for profit.
If you read this far, thank you from a fellow system for doing so.