Last time out, the Joker was a joke. Jared Leto's green-haired ghoul in Suicide Squad was the epitome of a cartoonish villain. But Todd Phillips' Joker, a dizzying origin story about Batman's nemesis, is the perfect antidote. Unveiled at this year's Venice Film Festival, Joker plays like an ode to 1970s New York and its cinema, with Joaquin Phoenix's Arthur Fleck a ticking timebomb. Living with his mother Penny (Frances Conroy), Arthur works as a professional clown – badly – and desperately wants to be a stand-up comic.

Like a mix between two classic Scorsese antiheroes – Taxi Driver's Travis Bickle and The King of Comedy's Rupert Pupkin – Arthur is one of the ignored. Taking seven different medications, his already-fragile mental state means he can burst out laughing inappropriately. Phillips and Scott Silver's script feels like a blatant attack on the American healthcare system, particularly when Arthur is told his regular counselling sessions are being terminated due to cuts.

While he dreams of meeting Gotham talk-show host Murray Franklin (Robert De Niro) or dating his neighbour Sophie (Zazie Beetz), Arthur's transition towards the Joker is utterly convincing, in a city stinking with decay, strikes and class divides. Of course, there are nods to Batman – his father Thomas Wayne (played by Brett Cullen) features in an intriguing subplot – but Phillips is largely restrained when it comes to dropping in fanboy Easter eggs.

Rather, what we have is the darkest comic book movie since Logan and the most daring since The Dark Knight, when Heath Ledger of course played the Joker to Oscar-winning effect. Utterly committed, Phoenix is astonishing as Arthur; you can see the cracks appear as he gradually finds his inner evil, the actor not once veering towards caricature. Equally Phillips, famed for comedies like The Hangover and Due Date, wows us with a grave vision he never swerves from. Unmissable.

Screening as part of the Venice International Film Festival 2019. General release from Fri 4 Oct.