Paul Haggis actually thinks movies can mean something, even change things. So, of course, critics like to crush him. Ambition equals pretension every time. Crash won the 2005 Oscar, but detractors tarred Haggis’ race parable for overreaching. Right. Feed us more pap, please. Haggis haters will have a field day with In the Valley of Elah. The title, referring to the spot where David slew Goliath, is a showy symbol. That’s Tommy Lee Jones, minus even a slingshot, as Hank Deerfield, a retired Vietnam vet taking on the whole Army to find out why his soldier son, Mike (Jonathan Tucker), is dead. Not in Iraq — Mike’s murder happened at home, near Fort Rudd, his base in New Mexico. Leaving his wife (Susan Sarandon) at their house in Tennessee, Hank drives off to get answers. And Roger Deakins, a virtuoso with lighting and camera, tracks him into the deepest shadows. The spare, ingrained purity of Jones’ work, here and in the upcoming No Country for Old Men, is astonishing. Want to see acting lifted to the level of art? This is it. Jones drives the film as Hank is stonewalled by military brass (repped by Jason Patric) and Mike’s soldier buddies (Wes Chatham, Mehcad Brooks, Victor Wolf and Iraq vet Jake McLaughlin). His only support is civilian cop Emily Sanders (a dynamite Charlize Theron), a single mom with her own issues. Flashbacks to Mike in Iraq, from his cell-phone videos, turn up disturbing evidence. But Haggis’ script, loosely based on a true story, isn’t about the war. It’s about the humanity being sucked out of the soldiers we send there, and how that process reflects on us as a nation. Yes, Haggis stumbles and loses focus. The haunting, heart-piercing Elah isn’t perfect. It’s something better: essential.