It has been said that William Friedkin found himself in the right place at the right time, but only on two specific occasions: the shootings of “The French Connection” and “The Exorcist.” This seems to sell short the accomplishments of a man often unjustly left out of the 1970s “Easy Rider/Raging Bull” clique. After all, he made “To Live and Die in L.A.”

    His new film — from a play by Tracy Letts — centers on Agnes (a more lusty than usual Ashley Judd), a waitress living a dead-end life with her main concern being the unannounced and unwelcome visits from her ex-husband (Harry Connick Jr.). Agnes has aspirations, but she likes her booze and her grass more than she likes her job or her ex. Judd plays Agnes with authenticity, eager for some kind of thrill or some kind of relief from her routine that eventually does come. It is perhaps her best performance to date in a career filled with hysterical damsel-in-distress mediocrities.

    When she meets Peter (Michael Shannon, reprising his stage role), things change significantly both for her character and the film. A psychological case study degenerates into an old school horror film with tentative special effects and a weak nod to the paranoia of the 1970s (wherein Friedkin’s reputation was made). Peter is a veteran who is convinced that a military experiment has left him with tiny insects crawling under his skin.

    This is a common complaint, of course, among drug addicts and sundry psychological casualties. So, the situation stands easily as a metaphor for anything from AIDS to imperialism to obsessive romantic love to pure psychosis, but the gooey special effects make it ever harder to take the premise seriously.

    Friedkin’s steady and masterful ramping up of the film’s tension gets dissipated even in the midst of some truly terrifying scenes.