Bad acting is something we’ve come to expect and love in horror movies along with slutty girls, victims running into the woods, and villains with tortured pasts. In fact, usually the acting is so bad that it creates humor and appeal in its ridiculousness — as in Grindhouse films. “The Last Exorcism,” however, sets itself apart in that it has flawless acting and a refreshingly original story. But, what it lacks is the kind of scares that make you sleep with the lights on.