As with every one of Lars Von Trier's previous films, this one arrives with an accompaniment of hype, hope and controversy.

Its two parts total four hours of Danish devilment, including numerous scenes of explicit sex presented with the brazenness of pornography, and a young heroine who pursues a self-loathing life of sex addiction, with some gasp-inducing S&M thrown in for good measure.

It is just a normal day in the office, then, for the man who gave us Breaking The Waves and Dancer In The Dark, The Idiots and ­Antichrist, cause célèbres all. Von Trier can't help but try to pull our chains.

As usual with him, the ­question is whether there is any point to the tease. Whatever you decide, if you embark on Nymphomaniac Part I you will almost inevitably want to see it through.

A woman lies beaten up in an alleyway in the snow. A middle-aged passer-by takes her back to his dingy apartment to rest. Joe (Charlotte Gainsbourg) declares that "I'm just a bad human being" deserving of her plight. But Seligman (Stellan Skarsgard) gives her tea and sympathy, and over the course of the night she recounts her life and career - for her lust seems entirely vocational - as a nymphomaniac.

What follows is frequently ­shocking, whether it is the very young child discovering her ­sexuality, the teenage Joe (played by newcomer Stacy Martin) making her way through a train with the aim of seducing as many male passengers as possible (leading to the film's first explicit sex scene), or Gainsbourg's older Joe - in the film's darker Part II, getting an almighty lashing at the hands of the mysterious K (Jamie Bell).

Running through her narrative are memories of her loving father (Christian Slater) and the difficult relationship with the man who takes her virginity, Jerome (Shia Labeouf).

But neither of these key male relationships inform Joe's attitude to men overall, or explains why she should feel so profoundly humiliated by the act of love. And while the film constantly returns to the erudite, asexual Seligman's attempts at analysis, they are so laughable - involving fly-fishing, religious symbolism, the Fibonacci numbers and knot-tying - as to only get in the way.

"I think this was one of your weakest digressions," Joe tells her host at one point, revealing that these often hilarious sequences are, indeed, the director's way of making fun of our need to explain or understand a narrative, and his unwillingness to help.

But this again prompts the question, why bother then? So much of the film feels like empty show.

A case in point is the explicit sex. The use of CGI to have actors' faces in the same frame as their body doubles' genitalia is a cheeky cop-out (if you want to be groundbreaking, then employ actors who are prepared to go all the way).

In any case, Von Trier's sex scenes contribute nothing to the psycho­logical insight that you would expect a world-class filmmaker to want to make.

Gainsbourg, whose face ­naturally carries a sort of battered pain, leaves the film's strongest impression, which is of extreme, bone-crushing loneliness. If only we could, after four hours, know a little bit more about that.

And yet while it does not deliver profundity, Nymphomaniac is one of Von Trier's most entertaining films.

Perhaps all he wants to achieve is a knowing, tongue-in-cheek encouragement to lighten up about sex. Tellingly, his piece de resistance involves nothing more risque than imagination, as a cheated wife - played with brilliant ferocity by Uma Thurman - barges into Joe's home with her children to confront the adulterers.

"Would it be all right," she asks, not waiting for an answer, "if I show the children the whoring bed?"