As the reviewers have said, this is very much an "M Night Shyamalan" movie in terms of style.
Its greatest strength is the performance of McEvoy (which was breathtaking), closely followed by that of Taylor-Joy.
Well worth a watch.
Forget the criticisms from the mental health fraternity regarding the portrayal of DID. I've seen far worse. And if you watch Shyamalan for the realism, you're looking in the wrong place anyway.