Early in W, Oliver Stone's new biopic about President Bush, the president (Josh Brolin) sits at the head of the White House dining table eating a ham sandwich. Vice-president Dick Cheney (Richard Dreyfuss) briefs him on "enhanced interrogation techniques". Dreyfuss plays Cheney as a malignant tutor in realpolitik to the younger man. In tones of extreme reasonableness (think of Dreyfuss in Jaws saying "this was no boating accident") he describes "fear scenarios" - but "nothing fatal" - and assures the president "you have the capacity to do anything you see fit". Bush is delighted that the torture briefing is "only three pages" and jokes, mid-mouthful, that it "sounds just like my fraternity days".

It's a gripping scene. As well as pungent dialogue and wonderful acting, especially from Dreyfuss, who nearly steals the picture, the film has a sharp eye for table manners. Brolin's president eats like a badly brought-up adolescent. Later, the first romantic lines he directs at future wife Laura (Elizabeth Banks) are muffled by the hamburger he is squeezing into his mouth. And he has the habit of eating and drinking at the same time. Overall the effect is funny and repellent. It signals moral disgust, too. Near the end the White House war experts conduct an anxious post-mortem on the invasion of Iraq and the missing WMDs. The camera lingers in close-ups of their forkfuls of fruit pie.

The Cheney-Bush dynamics recall Gordon Gekko's mentoring relationship with the Charlie Sheen character in Wall Street, which was co-written by W's screenwriter Stanley Weiser. Weiser even gives Cheney an exhilarating, borderline psychotic monologue just like Gekko's "greed is good" speech. In this case he's in a dimly lit war cabinet, in front of a map, revealing his plan for world domination through controlling the energy reserves of Eurasia. This is the heart of the story. Iraq, Cheney says, "the fertile chokepoint of civilisation" is "floating in a sea of oil" while Iran is "the mother lode". "Control Iran," Cheney says, "control Eurasia. Control Eurasia, control the world. Empire! Real empire! Nobody will f--- with us again."

W begins with Bush and his war cabinet sitting on White House sofas dreaming up the phrase "axis of evil" and thinking of a pretext for the second Iraq war. Scott Glen has the scrawny look of "Rummy" Rumsfeld and Thandie Newton appears to have had her face re-moulded to make her closely resemble Condoleezza Rice. Jeffrey Wright's Colin Powell comes over as a good man - "That's not a new world order," he tells Cheney after that Eurasia speech, "that's a world gone mad!" But even he is compromised by political expediency. The exchanges between Powell and Cheney crackle: both of them carry baggage from the administration of Bush Snr. Tucked away in the background at these war meetings is soft and slippery Karl Rove (Toby Jones), the old friend, at once bullying and obsequious towards Bush.

The screen dissolves to Bush's alcohol-drenched memories of his fraternity, with savage preppies enacting rituals involving funnels of vodka. It proceeds like this with flashbacks to Bush's earlier life, interspersed with the lead-up to war, the search for "red meat" on Saddam's weapons programme, and the post-invasion hunt for vanished WMD. Stone sticks mostly to aspects of Bush that no one disputes. He allows himself to speculate that one of the driving forces inside the younger Bush was emotional conflict with his father. In this analysis, the second Gulf war was "junior" finishing the business that "pappy" started in the first Gulf war but didn't have the gumption, as his son sees it, to carry to its end. Stone treats the struggles of the young Bush with sympathy. James Cromwell, Prince Philip in The Queen, is an austere Bush Snr, endlessly disappointed. The young Bush refuses to settle in any of the jobs his father fixes up - the sports store, the investment bank, the oil-rig job. Stone doesn't make any mileage out of Bush's drink-driving or his service in the Air National Guard or drugs. Bush's conversion, under the guidance of a pastor (Stacy Keach as a deep-voiced godly giant), becomes the central event of his life. Bush Snr thinks the born-again Christian style in politics looks "insincere".

W is often funny and contains some outstanding performances, although it suffers from being slightly too long. What's interesting is how Stone, a famous Left-winger, has disappointed some critics by pulling his punches. Actually, all he does is invite us to view Bush as a real person. It's a subtler approach than those of Stone's earlier films (Born on the Fourth Of July, JFK) which are notable for cardboard characters, untruths, sensation and bias. From time to time, Stone cannot resist manipulating: for example, to illustrate the point that Bush is a cowboy he shows the bombing of Baghdad to the tune of "The Yellow Rose of Texas". But on the whole he resists caricature and allows Bush a degree of complexity (more than he grants to Cheney). Is it conceivable that history will judge the truest contemporary account of Bush to have come from raging Leftie Oliver Stone?