As America awakes this week from the nightmare of the past eight years and the world exults in the historic election of Barack Obama, Oliver Stone delivers his biopic of the man Obama is replacing, the man who has a strong claim to be the worst president in US history  - George W. Bush.You’d imagine that Stone would have seized the opportunity to discharge a fusillade of caustic satire, furious lampoonery and savage burlesque. Far from it: W. is actually a good-humoured, surprisingly compassionate, almost sympathetic portrait of America’s 43rd president.Yes, America’s president. The leader of the free world - how on earth did someone so manifestly inadequate get the job? How did this party-loving, draft-dodging frat boy, this failed businessman forever bailed out by his family, ever get himself elected US president? That’s what Stone’s movie attempts to answer.W begins with the build-up to the Iraq invasion, showing Bush – uncannily impersonated by Josh Brolin – at the helm of his war cabinet, and then flashes back and forth to various stages in his journey to the White House. We get to see the cocky Yale graduate, the drunken twentysomething, and the would-be businessman, forever lurching from one disastrous venture to the next, and forever hoping to impress his father, a stern and patrician George Bush Sr played by James Cromwell.And we get to see how Bush finds God, gives up the booze, marries Laura (Elizabeth Banks) and turns his life around. But Stone also shows us how Bush’s ambition – driven largely by his efforts to prove himself to his father, and then outdo him, a weirdly Oedipal relationship – eventually landed him in a role to which he was hopelessly unsuited.It’s a fascinating story, and Stone tells it entertainingly, but while I was watching I found myself regretting his restraint. There are satirical touches – one sequence shows Bush and his cohorts (including Thandie Newton’s Condoleeza Rice and Scott Glenn’s Donald Rumsfield) getting themselves lost in the cou