It seems fairly safe to assume that being Charlie Kaufman may not be a lot of fun. The screenwriter of Adaptation, Eternal Sunshine of the Spotless Mind and Being John Malkovich has premiered his directorial debut in competition in Cannes, and it gives an insight into the workings of his mind. The bitter humour that characterises the first half of Synecdoche, New York gives way to an engulfing melancholy and paralysing regret about wasted opportunities, creative failure and the tragic impermanence of everything we value. At times it feels more like a suicide note than a movie.

Kaufman's talent as a writer has secured him a first rate cast. Philip Seymour Hoffman plays Caden Cotard, presumably Kaufman's alter-ego. Caden is a creatively repressed theatre director, whose artist wife, Adele (played by Catherine Keener), is rapidly becoming a stranger and whose niggling hypochondria is warping into a fully fledged obsession with his own mortality. A man increasingly unmoored in his own life, Caden's one connection with the world comes through a tentative, tender flirtation with a theatre box-office clerk called Hazel (Samantha Morton, a delight). But while it becomes increasingly clear that Adele has written him out of her own story, Caden seems unable to grasp at happiness with Hazel.

Meanwhile, his body is plagued by bizarre and unsightly complaints.

It is around this point that the film becomes surreal. Caden is awarded a grant that permits him to embark on his life's ambition - to create something real and true. To this end, he decamps from his home in Schenectady in upstate New York to Manhattan, where he takes over a cavernous warehouse. Within it, he sets about creating a replica of the city outside, complete with an ever-expanding cast acting out the mundane, day-to-day activities of the characters they have been assigned.

Caden is, at first, omnipotent, imperiously determining daily destinies with curt instructions on slips of paper. But as the years role on with no indication that the play will ever be finished or that an audience will ever witness it, the production takes on a life of its own and Caden, Hazel and the actors playing Caden and Hazel become characters in a increasingly complicated plot. As first one, then another actor plays Caden Cotard, the real Caden begins to lose his identity; with that comes the realisation that he is both replaceable and forgettable.

Synecdoche, New York is a defiantly uncommercial movie - it's infuriatingly enigmatic, philosophical and nobody knows how to pronounce the title. Plus it is about death. The ambition is staggering. I'm not sure it works entirely. While Kaufman does a sound job as the director - he is particularly nimble when guiding us through a flipbook of alternate “realities” - his writing, with its onslaught of crackpot ideas, always runs the risk of dominating any film that doesn't have an experienced director with a very confident aesthetic.

There's a certain irony that in order to create something real, Caden ends up with layer upon layer of artifice. But there is, unquestionably, an emotional authenticity to Kaufman's vision - a profound and very affecting sadness that rings out pure and clear.

Editor's choice

• U2 at Nou Camp Stadium, Barcelona
• The 50 Best Movie Villains
• The 15 golden rules of theatre etiquette