A couple of nights ago, I saw There Will Be Blood, a grim, and undeniably powerful movie about a California oil man. It stars Daniel Day-Lewis. I always measure the power of a movie if I wake up the next day and think about it. And when that happens, I often seek insights from the Post-Intelligencer's William Arnold. I wasn't disappointed. I got to know Arnold in the 1980s, when I worked at the P-I as its theater critic. I was in awe. I still am. Writing reviews year after year is unbelievably hard work. It's easy to go stale or get lazy. And yet, then and now, Arnold packs more into a 600-word essay than nearly any critic I know. A newspaper critic's job is to announce a film, report on what the work is trying to do, say whether it succeeds on its own merits, and give a recommendation. Arnold does that and more. Many of his reviews put the film in a larger context -- the history of a genre, the work of a director, the evolution of an actor, or a trend in the industry. So you come away from an Arnold review not only knowing something about the film but also something larger about the art. He does so with an accessible writing style. For a long time, Seattle had two strong movie critics -- Arnold and his colleague at the Seattle Times, John Hartl, who retired from daily reviewing a few years back. I don't always agree with Arnold's reviews, but that's not the point. I've read him enough to know what his tastes are and to make up my own mind. I trust him. I've heard stories about how Arnold's work is closely followed by people in Hollywood. I'm not surprised. He's one of the best in America.