Some people find this twisty and twisted psychological thriller arty and pretentious. I find it arty and provocative. Whichever way you go, you will find yourself in thrall to Naomi Watts. The raw power of her performance is all the more remarkable when you realize that her character, Lila, a troubled artist, is on the fringes of the story. The deft script, by David Benihoff (25th Hour), concerns Sam Foster (Ewan McGregor), a Manhattan shrink trying to stop a patient, Henry Lethem (Ryan Gosling), from making good on a threat of suicide. Director Marc Forster (Monster's Ball, Finding Neverland) makes good on the script's promise by creating an alternate universe as Sam begins to live in the world of Henry's delusions. As the film takes dark, hallucinatory turns, it's Lila — she once threatened to kill herself before Sam became her doctor and lover — who provides emotional ballast. Forster's visionary brilliance demands and gets uncommon depth and subtlety from the actors. But it's Watts who guides us home. Stay with her.