Not quite Signs or SIxth Sense.

Rating: Null/10 (19 January 2017)

"He's done awful things to people and he'll do awful things to you." Kevin (James McAvoy)
So warns one of a couple dozen personalities played by a game and convincing McAvoy, whose 23 Dissociative-Identity-Disorder (DID) central characters people the messy Split. Director/writer M. Night Shyamalan has crafted an abduction thriller cum multiple personality disorder with his signature twisted ending, but overall not near the greatness of The Sixth Sense, Signs, or even the more recent The Visit.
Three teens are abducted by Kevin et al., whose promise that a "Beast" is coming to devour them does spook the bejesus out of them. The more canny of the three, Casey (Anya Taylor-Joy from the surprisingly effective The Witch), is the heroine destined to grapple with that Beast and the personalities that wander around this bunker-like world (Remember the locale of 10 Cloverfield Lane?) The director directs way too many close-ups of her for my taste, and the usual horror tropes like jump scares aren't sufficient to mask a fragmented plot that mirrors the split personality disorders. Outside forces like the kindly shrink, Dr. Karen Fletcher (Betty Buckley), are actually peripheral to the power of Dennis and his army of identities.
Brian De Palma's Dressed to Kill used a split personality motif to explain bad behavior; Hitchcock, a big influence on De Palma and Shyamalan, used most of Split's bag of tricks, especially in Psycho, long before Shyamalan knew what personality was; United States of Tara showcased for TV the DID state to some notable success. Split will not meet the "classic" criteria they have achieved.
Because payoff for Shyamalan has always been the twist ending, he doesn't so much disappoint as confuse, with unfortunate explanations that sap the challenges a smart thriller should offer.
"I've never seen a case like this before. Twenty three identities live in Kevin's body." Dr. Fletcher