A convicted criminal facing his last night of freedom takes a long, hard look at himself in a restroom mirror. Filled with horror at his impending prison sentence, and weighed down by the mournful malaise that seems to have infected New York in the wake of 9/11, Monty Brogan (played by the irrepressible Edward Norton) squares up to his own reflection and lets fly a stream of bile-ridden invective against the inhabitants of his home town. Spewing sardonic spite, Monty (whose harmonious biracial relationship is about to be replaced by the threat of cell-bound molestation) rails against New York's melting-pot population. It's a montage of human life in caricature, providing a snapshot of sneering contempt that is both gaspingly shocking and alarmingly funny. Bernard Manning would have choked on his popcorn.
Three things are notable about this tirade, which forms the centrepiece of the new movie 25th Hour, adapted from David Benioff's first novel. First, the demonic alter ego that momentarily possesses Monty is an equal-opportunities bigot, damning every race, religion, creed or colour with the same unmediated misanthropy: the anger is wholly inclusive. Second, this jaw-dropping invective is crucially self-reflexive, with Monty (on the eve of his exile from New York city life) reserving his most resounding "fuck you" for himself. And third, the film in question is directed by Spike Lee, spokesman of the so-called "new black cinema" thanks to overtly political feature films and documentaries such as Malcolm X (1992), Get on the Bus (1996) and 4 Little Girls (1997); and a legitimate contender (alongside the likes of Woody Allen, Martin Scorsese and Abel Ferrara) for the crown of New York's cinematic poet laureate, courtesy of elegiac "Big Apple" features like Clockers (1995), Summer of Sam (1999) and Do the Right Thing (1989).
A Spike Lee film (or "Spike Lee Joint", as he annoyingly prefers to call them) has always been a troublesome affair, sparking admiration and confusion in roughly equal measure. From the earliest days of the acclaimed indie hit She's Gotta Have It (1986), which a feminist friend of mine labelled "muddle-headedly macho", to the headache-inducing meanderings of Crooklyn (1994), which prompted press-screening complaints about the projectionist using the wrong lens (apparently, the picture was meant to be all bent out of shape like that), Lee's films can usually be relied upon to get under somebody's skin. It was ever thus - as a first-year film student at NYU in 1980, Lee made a ten-minute short entitled The Answer, which was intended as a riposte to D W Griffith's Birth of a Nation (a cinematic milestone marred by its unabashed glorification of the Ku Klux Klan), and allegedly almost got himself thrown out of college in the process. A few years later, his graduation film, Joe's Bed-Stuy Barbershop: we cut heads (1982), won the Student Academy Award.
Over the next 20-odd years, Lee's extraordinarily prolific film-making career has taken in a head-spinning tour of highs and lows, boasting more ups and downs than the Coney Island roller coaster. On the upside, he has courted widespread press attention and audience attendance with films such as Malcolm X, which broke out of the reviews sections and on to the news pages; and picked up Oscar nominations for 4 Little Girls and Do the Right Thing, both of which rank among his best work. (Do the Right Thing was recently voted one of the best films of the past 25 years by the British Film Institute's Sight and Sound magazine). On the downside, offbeat pictures such as Crooklyn would be largely overlooked in the US, and then shuffle out on to the British video market without troubling the mainstream cinema circuit. In this business, it seems, even notoriety is no guarantee of financial success.
Looking back over Lee's oeuvre, which is currently the subject of a Barbican retrospective, what is most notable is the way in which he has managed time and again to sidestep the mantle of comfy, revered admiration, succeeding instead at constantly putting the ideological cat among the pigeons. Monty's central speech in 25th Hour (which features in Benioff's novel, and was included in the film's screenplay at Spike's insistence) is no exception. Lee's movie-making legacy includes something to rattle everyone, from the Italian-Americans who objected to alleged racial stereotyping in films such as Do the Right Thing, Jungle Fever (1991) and Summer of Sam (pizzeria owners; guilt-ridden mama's boys; homophobic racists; lunk-headed Lotharios) to the women who remained unimpressed by the alleged "female perspectives" of the likes of She's Gotta Have It and Girl 6 (1996) - the former getting tied up in knots about the true meaning of female sexual liberation; the latter including an infamous "movie audition breast-baring" episode seemingly designed as much to alienate as elucidate.
More troubling have been the charges of anti-Semitism, which date back to films like Mo' Better Blues (1990), with its scathing depiction of Jewish nightclub owners, and which have since been fuelled by the occasional ill-judged, offhand comment in the press. (Lee once told me in a radio interview, for example, that he knew his excellent documentary 4 Little Girls wasn't going to win an Academy award because it was up against "a Holocaust movie" and one of the makers of that film was a rabbi. "I knew it was over," he drawled. "O-vah!"). Most bizarrely, Lee has even managed to annoy members of the New York Civil Rights Coalition, who recently took offence at his use of images of blackface minstrelsy to publicise the media satire Bamboozled (2000), prompting the NYCRC director, Michael Meyers, to accuse him of "recycling racial trash" in an attempt to "raise racial anger again - which is his trademark". Meanwhile, the New York Times refused to run ads for the film, claiming that they would "offend our readers".
Personally, I remain more impressed with Lee's controversial "failures" (Bamboozled may be a mess, but what an intriguing mess it is!) than with his more widely feted successes (Bill Cosby, Michael Jordan and Oprah Winfrey all reportedly coughed up cash to ensure that Spike got final cut on Malcolm X, but I am still with the studio executives who thought that three and a quarter hours was way too long). And despite the outcry from relatives of the serial killer David Berkowitz's victims, claiming that their personal tragedies were being exploited, I would still fly the flag for Summer of Sam as one of Lee's finest films to date, a multilayered portrait of New York City in 1977. It comes as close as any recent film to capturing the vibrant, cross-cultural madness of that city at that moment.
As for 25th Hour, I remain reassuringly uncomfortable about its use of post-11 September imagery (a title sequence of twin memorial searchlights piercing the New York skyline; a key location overlooking Ground Zero), which may be either bravely symbolic or mildly opportunistic. The fact that I can't decide one way or the other - in just the same way that I can't figure out whether his recurrent visual tick of placing actors on a moving platform is quaintly endearing or just plain silly - reassures me that Lee has lost none of his power to provoke. In the end, it is this very uneasiness that makes a Spike Lee film (sorry, "Joint") such an unmissable proposition.
Prepare to be perplexed.
Spike Lee: the full retrospective is at the Barbican, London EC2 (020 7638 5403) until 24 April
Mark Kermode is a film critic. He contributes to Sight and Sound, BBC Radio 5 Live and BBC2's Newsnight Review