Michael Moore’s stock has fluctuated wildly over the last six or so years. Where in the late 1990s he held a modest reputation as a documentary filmmaker, in the UK he was barely known.

After all, his breakthrough documentary Roger Me – a 1989 investigation into the impact of outsourcing jobs to foreign countries in his hometown of Flint, Michigan – seemed to be looking at problems far less serious than those facing people in post-Miners’ Strike Britain on the eve of the Poll Tax Riots.

He had picked up a few fans through his cult TV shows TV Nation and The Awful Truth – interestingly original mixes of satire, regular comedy and proper investigative reporting that went on to inspire the likes of Louis Theroux (who got his first break on the show) and British activist comedian Mark Thomas – but as Bill Clinton left office, Moore could barely even count as an F-list celebrity.

With 2002′s Bowling for Columbine, his Oscar-winning documentary on American gun culture and first film in five years, the Bush administration was only a secondary target. Yet Columbine’s controversy and success amongst the millions of disenchanted Democrats who felt the presidency had been stolen from them in the 2000 elections showed Moore the right direction for real attention.

So came Moore’s rant against the war against terror, Fahrenheit 9/11 – one of the most vehement mainstream attacks on the policies of a sitting president in America’s history, the first documentary to win the Palme d’Or at the Cannes Film Festival, and the highest-grossing documentary of all time. With the movie’s massive success, Moore swiftly became one of the leading voices of the American left in the run-up to the 2004 presidential election. His humour-filled attacks on the Bush administration were almost impossible to avoid, even in the UK.

With that massive profile, naturally enough the backlash began. Having become so prominent, Moore was naturally a target for smears and attacks by the American right, yet his vehemence in defending himself and arguments against his attackers soon began to grate even with those loosely on the same political side. Much as with President Bush himself, Moore found himself in a position where people either loved him or hated him. In the process, having become a part of the story, his message began to get lost.

Now, halfway through Bush’s second term and three years after Moore’s last film, rather than continue with another look at the war against terror, the director has instead turned his attention back to his roots, and a problem that affects the lives of ordinary Americans – the US health care system. All of which is likely to be of significantly less interest to Brits – especially as by now we’ve all heard of Moore’s intriguing take on the NHS, seemingly being under the impression that it’s efficient and well-run.

But Moore has retained his knack for identifying with the little guy, even while exploiting their pain to make his point. His documentaries were always more polemical than factual, and consistently skilfully constructed. The fact that he remains likeable despite his hugely raised profile, and that his humour can emerge even amongst the unpleasantness of people dying through lack of health insurance, is testament to his skill as a filmmaker – a skill that’s been all to easy to forget during his time as self-appointed Bush-basher in chief.