The screen is black. The soundtrack is screams, shock, suffering. The audience, laughing a moment before, sits in uncomfortable silence. In the dark auditorium, against the empty screen, everyone can see the planes plunging into the Twin Towers. The projectors are in our minds. This is a masterful moment of documentary filmmaking and - not for the last time in Michael Moore's Fahrenheit 9/11 - I can feel my eyes filling with tears. The buzz film of the festival - the film its maker hopes will bring down George Dubya Bush - has arrived. But it will not win the Palme d'Or.

Perhaps because Moore rushed the production in order to premiere at Cannes - and is desperate to release the picture before the US presidential election - his latest polemic feels a little flabby, a little unfocused. It lacks the edge of Bowling For Columbine, where the anarchic, sprawling style suited the intractable nature of the subject matter.

Is Bush an idiot or evil? Moore appears to believe the former, but then portrays his regime as coldly manipulative and money-grabbing: prepared to do anything to advance their business needs. I wonder if the image of Bush as Mindless Ape doesn't work in favour of the president, making him a figure of fun, even as his orders lead to mass murder in the Middle East: bodies blown bloodily asunder by cluster bombs and oh-so-subtle tanks.

It is in Iraq where Fahrenheit really burns. The leisurely pace of the first act - where the business dealings between the families of Bush and Bin Laden are explored - is replaced by urgency and aching sorrow, with footage usually deemed too strong for Western eyes: a child's broken body, a grief-stricken woman wailing at the camera, the devastating after effects of supposedly accurate US attacks. But Moore's primary interest is America - and the effect on his home country of its overseas actions.

Perhaps aware that he won't win the Democrats votes by focusing on the grief of some sand-skinned foreigner, he returns to the States to follow an American mother mourning her son's death in Iraq. Lila Lipscomb's story is strong, moving and brave. It is certainly the story Moore should tell if he hopes to topple Bush at the election. But it is sad that even a lefty filmmaker feels - knows - he needs to concentrate on (proportionately slight) Western losses, because it may be hard for people to care about the thousands of darkies our nations are killing as a matter of course.

Lipscomb's horrendous experience is obviously relevant, however, whereas an interlude examining America's shoddy "homeland security" just diffuses the focus of the film. But I wouldn't want you to think Fahrenheit 9/11 is a failure. It is provocative, entertaining, shocking, upsetting and blackly comic. It will be revelatory to those unfamiliar with Moore's writing or the already well-documented facts of corporate war profiteers making cash out of carnage in Iraq. For bringing politics into primetime, taking an important message to the masses, in however haphazard a manner, Moore is to be admired and his movie - whatever its flaws - must be seen.

Which is more than can be said for The Ladykillers. Thanks to Paul Tompkinson for writing in to ask if the Coens "have truly gone off the boil" with their remake of the Ealing classic. The anwer? They're simmering. The film isn't the disaster some have suggested; it simply feels unnecessary, with Tom Hanks taking the Alec Guinness role of a nefarious professor who must off an old lady to get away with a heist.

The original, often tagged a comedy, actually has limited laughs. It's a macabre little tale which is occasionally uncomfortable viewing. The remake is more broadly amusing, but it never for a moment feels real. And it also relies a lot on racial stereotyping and profanity for its laughs, in a manner which would not be tolerated by more liberal critics if undertaken by anyone other than the darlings Coens. Hanks will be trotting down the red carpet later today and I'll let you know if he has anything interesting to say. In the meantime, you can catch up with the characters we met at the beginning of the festival, for their opinions on Fahrenheit 9/11, breaking down in screenings, and whether this is a vintage year.