Story, so the experts say, is the essential element of any successful screenplay. Compelling characters and engaging dialogue are certainly nice, but to get your movie made, traditional wisdom (usually in the guise of studio executives) dictates that you must have a story worth telling. Steve Zaillian, writer and director of “All the King’s Men,” is a man who has clearly taken this advice to heart. The Oscar-winning screenwriter of “Schindler’s List” (1993), “Searching for Bobby Fischer” (1993) and “A Civil Action” (1998), Zaillian has long shown a knack for finding and adapting gripping narratives.

“All the King’s Men,” based on the Pulitzer Prize-winning novel of the same name by Robert Penn Warren, has already inspired one highly acclaimed cinematic version; however, Zaillian has gone on record claiming that he has never seen the 1949 Robert Rossen film and that his own film is a direct adaptation of Penn Warren’s work. Despite the inclusion of the occasional color spectrum change or adventurous long shot, Zaillian, true to his calling as writer, not director, tends to stick to the story, and stumble though he might, he does not ruin it.

The film, like the novel, tells the story of Willy Starks (Sean Penn), a populist Louisiana politician believed to be based on former Gov. Huey Long. Starks’ tumultuous rise from local treasurer to a governor with presidential aspirations is narrated by newspaperman and eventual employee Jack Burden (Jude Law). Law and the rest of the all-star supporting cast turn in solid if unremarkable performances, bringing the corrupt world of Southern politics to life. The standouts are James Gandolfini, who seems to have channeled all the immoral energy of Tony Soprano into his portrayal of dirty politico Tiny Duffy, and Anthony Hopkins, whose Judge Irwin possesses the charm and ominous presence of Hannibal Lecter. The film’s female characters — most notably Sadie Burke (Patricia Clarkson), Starks’ jealous girlfriend, and Anne Stanton (Kate Winslet), Burden’s childhood sweetheart — are one-note weak women. Zaillian is not to blame for this flaw, though; Penn Warren’s sympathies and interests clearly lay with the story’s men.

What Zaillian should be blamed for is the failure to recognize the true power of the novel. That power is not derived from the supporting players or the evocative picture of the south, but rather from the sheer force of the driven, awe-inspiring and self-destructive Starks, and to say Zaillian missed the boat on this one would be a gross understatement. Few miscasts have been as egregious as that of the chronically overrated, constantly contrived Penn as the raw, unrefined firebrand Starks. Penn’s brand of anguished overacting may have a place in the personal drama — say “Mystic River” (2003) or “21 Grams” (2003); here, though, he comes off as painfully insincere, even if well-intentioned. Considering his extremely public opposition to the Bush administration, we cannot escape the suspicion that Penn is playing the populist-as-savior role as a way of further expressing his own distaste for the corporatization of government or even advancing a possible political career. Even so, we might be able to sympathize if it weren’t for the fact that Penn constantly seems to be pandering to the audience.

Zaillian’s reliance on cliches and bombastic rhetoric in constructing Starks’ dialogue certainly doesn’t help, but Penn seems sort of ridiculous. Granted, most of the Southern accents sound canned, but Penn’s is unusually painful. As he cries out to the enraged masses that he will “nail up” the politicians who seek to exploit the common man, Penn’s body language and facial expressions suggest physical comedy as opposed to fervor. The Starks of the novel is a common man made larger than life, but Penn never begins to resemble the common man. Perhaps there is some irony in the thought that what eludes Penn in his portrayal of the populist is populism itself: The man devoted to expelling the privileged cannot escape his own privilege. Starks tells us that he’s “a hick” as a way of establishing credibility, but watching Penn, we just can’t believe it.

Ultimately, the real star power here lies not with Penn, but with Penn Warren. Remake or not, this is merely a competent film, and it is rare that competence is sufficient to produce an entertaining and moving movie. Had Zaillian played his cards right, he would have had an Oscar contender on his hands, but as it is, we are left with an adaptation of a political thriller. Luckily for us, it happens to be a damn good one.