With Sicko the director touches the delicate note of privatised Health Care System in the United States (the HMO is a powerful political lobby in U.S.) and it gives it the Michael Moore treatment, that is to say he puts in the picture a few willingly provocative twists and turns, that this time are summarised in a trip to Cuba to supply the needed medical treatments to those 9/11 volunteers, who saw the HMOs denying them cures to their serious illnesses caused by the toxic wastes of Ground Zero. The aim was to bring the 9/11 heroes to the American territory of Guantanamo to have them get the same excellent care and treatments Guantanamo terrorists get; not succeeding in his effort, Moore got side-tracked into going to a Cuban public hospital, where (arguably, i dare say) the care is shown to be of better standards than the American one. In one precise blow Moore did what Moore is best at: igniting the fuse of controversy.
On the critics' side, besides any comments on the merits of the film and the obvious political battles, one must note that Moore does not get much sympathy from the very non-fiction community he belongs to, many directors (among which the founding fathers of non-fiction filmmaking) feel outraged by his improper use of the non-fiction tools to push his own personal goals and political ideas. A few indicators of this tendency are to be found in Moore's habit to always appear in his own work (in fact he even figures in all of his film posters) as main carrier of the narrative, interviewer and voice-over, which defies all laws of good non-fiction practice. Cannes might love "troublemaker" Moore, but his informed peers are critical of his "un-orthodox" methods; besides, I dare any journalist, on and off La Croisette, to not have doubt that bringing up the story of the Governmental treats almost 20 days after the letter informing Moore of the investigation was issued, might be a smart "publicity" stunt to promote the film among distributors and avoid it to be confiscated (just like it happened with Fahrenheit 9/11).
Forgetting all comments and doubts, the truth of the matter is that Michael Moore is an awfully good filmmaker, who's able to twist and bend the boundaries of documentary to his own will. Even though criticism is correct in ditching his work as one-sided, nevertheless watching his films is still a good (and effective) cinematic experience. All is left to do is to wait and see if also Sicko will make it to the Cinemas.
related links: Moore's website - CNN article praising Sicko - Entertainment Weekly interview on Sicko - video interview to Jacques Cousteau in Cannes 1956