Identity is a true underrated gem of a psych-thriller. I'd even say it's the perfect psych-thriller in concept.
Multiple killers trapped inside the same mind and the psychiatrist's brilliant plan to pit them against each other so they get knocked off one by one and the prisoner can salvage some sanity.
Really loved how the movie treated each identity like a potential killer or victim.
Most people thought it was a major cop-out that everything was happening inside the killer's head, I thought it was brilliant.