A career-best for Michael Keaton (Ed Norton and Emma Stone aren't too shabby either), this Charlie Kaufman-esque oddity from Babel and 21 Grams director Alejandro González Inarritu is a head-scratching delight.

Riggan Thompson (Keaton) is an actor famous for his Birdman super hero trilogy back in the nineties; he refused to star in a fourth instalment and his career went into freefall (Keaton's casting doesn't go unnoticed considering his career path post his decision not to return for Batman Forever). Riggan's attempt to be taken seriously by adapting Raymond Carver's What We Talk About When We Talk About Love for the stage is coming unstuck, however: pretentious method actor Ed Norton is a wildcard; girlfriend/actress Andrew Riseborough might be pregnant; New York Times theatre critic (a prickly Lindsay Duncan) is threatening to "destroy" the venture with a devastating review; and daughter Emma Stone is a recovering addict who could fall off the wagon at any moment.

Oh, and he also has super powers.

While Riggan's personal and professional problems are most definitely real there is a question mark over the legitimacy of his telekinesis and ability to fly. Is this a symptom of a nervous breakdown brought on by pressure of a fast-approaching opening night, or is the growly voice in Riggan's mind wishing he realise his true potential a bona fide super alter ego? González Inarritu plays around with this, fuelling both sides of the argument: Riggan admits to his lack of sleep in one scene but in the next a witness sees him jump from a building. The last shot will encourage debate no doubt.

Unfolding in a simulated single shot, the camera moves from the stage to the dressing rooms to the narrow hallways in the bowels of the theatre in an ever-moving flow. But this isn't simply to wow the audience, as its reason for being transcends the impressively executed gimmick. It's here to show how the mind, and in particular Riggan's increasingly erratic one, seamlessly unfolds: there are no full stops, no pauses, no fades to black as it moves from thought to thought, scene to scene. The style gives the scenes a manic energy, helped by the incessant freestyle jazz drumming, which gets more and more intense as Keaton grows ever twitchier.

While we engage in guesswork re the mental state of the protagonist, Inarritu busies himself with more important work, exploring the creative process, questioning why writers, artists, etc. do what they do. Are they motivated solely by the childish desire to be noticed, a simple hunger for fame and appreciation? Is it validation? It's tough to get at the answers as Birdman doesn't allow itself a moment to ponder: a busy thing, it's hectic scene after hectic scene with Inarritu cranking up the pressure all the time.

And it's funny, blackly funny - a parody in the vein of Living In Oblivion, Birdman is unafraid to take pot shots at itself.