Joaquin Phoenix stars in Her. Warner Bros.

Spike Jonze's fourth film, Her, has a deliciously ambiguous title that cuts straight to the heart of what the movie is about.

The sci-fi tale about lonely writer Theodore Twombly (Joaquin Phoenix), who falls in love with an artificially intelligent operating system (voiced by Scarlett Johansson), is light-years ahead of the likes of Siri and Samsung's S Voice.

On the surface Her could be an incredibly high production episode of TV series Black Mirror, but where the movie so triumphantly succeeds is in being both an original and refreshing twist on the rom com, and an insightful statement about our current relationship with technology.

Joaquin's Theodore cuts a lonesome figure; his thick moustache and hipster fashion sense never taking you away from those sad deep blue eyes.

His career is focussed on writing poignant personal letters for other people while he's still nursing a broken heart after a failed marriage to childhood sweetheart Catherine (Rooney Mara).

Theodore jumps at the chance for companionship when a new highly advanced personal assistant called Samantha, hits the market. Over time he bonds with this intelligent avatar and falls in love.

So, the movie is a kind of boy meets girl set-up, the difference here being that the girl, the 'her' in question, never appears on screen.

Particularly extraordinary is that around 95% of the time, Joaquin Phoenix is effectively talking to himself.

Pheonix's astonishing turn in The Master cemented his status as one of the great actors working today, and his performance here in almost a completely opposite role is just as magnificent.

Equally compelling is Amy Adams as his long-suffering friend and Rooney Mara as his venomous ex. But it's the performance we don't see on screen that's most remarkable. The vivacity Scarlet Johansson brings to Samantha is incredible. Not since HAL has a voice in cinema sounded so iconic.

Unlike either the clean and sterile or dank and grungy look usually employed in science fiction films, for this flick Jonze presents a retro-future vision of Los Angeles that could come straight out of an Ikea catalogue.

The super-saturated yet minimalist colour palette perfectly presents a utopia that isolates the melancholic Theodore. And in its over-designed artificial gloss it shows a contradictory existence that mirrors the film's story, both warm and cold, intimate and detached.

The vivacity that Scarlet Johansson brings to Samantha is incredible. Not since HAL has a voice in cinema sounded so iconic.

From a tunnel inside a Hollywood star's head in Being John Malkovich, to an unruly child finding himself in a land of monsters in Where the Wild Things Are, director Spike Jonze has always been interested in people who escape into their own fantasies.

Her might not be as radical, but its depiction of Theodore as a man not prepared to commit to the intricacies of human relationships, choosing instead to spend time with a computer in his high-rise apartment, is another example of a figure retreating in to a world of their own creation.

The best science fiction holds up a mirror to our current times, and the film's depiction of how technology has both infiltrated and shaped our social interactions feels particularly astute.

But there's never probing commentary or snarky cynicism here; Jonze makes us want to feel the future, not think it. Amy at one point tells Theo, "I just want to be allowed joy," and the movie certainly delivers that in spades. This is a picture impossible not to fall in love with.

Her will be released in cinemas nationwide from 14 February.