In addition to being surprisingly romantic and moving, Spike Jonze’s “Her” is also utterly frightening and sad. A deeply-felt fable of a love affair between a man and his artificially intelligent computer operating system, the premise may sound gimmicky.

The sight of Joaquin Phoenix wearing a moustache and weird pants might lead you to believe that this movie is another quirky comedy like “Being John Malkovich” or “Eternal Sunshine of the Spotless Mind,” but it is, in the end, serious and heartbreaking.

Joaquin Phoenix plays a ghost-writing divorcee who falls in love with a computer operating system in Spike Jonze’s ‘Her,’ now available for streaming or on DVD.

Joaquin Phoenix plays a ghost-writing divorcee who falls in love with a computer operating system in Spike Jonze’s ‘Her,’ now available for streaming or on DVD.

Joaquin Phoenix plays Theodore, a heartbroken man in the midst of a divorce from his beloved wife, who is played with great depth and intelligence by Rooney Mara. His job is to write letters for other people at a business called beautifullywrittenletters.com, and he spends all evening playing a video game that almost resembles technology we have now, but is interactive beyond current capabilities.

Jonze’s details are set in a very realistic near-future and set the stage for the arrival of “Samantha,” the operating system voiced by Scarlett Johanssen.

Everything you may have read about how warm and alive her voice is as a character is true. She existed instantly, both for Theodore and for us.

He wears an earbud and carries a little camera and they quickly begin to spend a great deal of time “together.” Soon, Samantha, whose intelligence grows and evolves constantly, despairs of lacking a body.

While the intimacy of Theodore’s relationship with Samantha is at the heart of the plot, the background story fills it in and makes it believable. While it is a story about him and her, it is also about the society they live in.

Amy Adams plays Theodore’s best friend and through her we learn that human/OS relationships are not too unusual and many humans find the possibilities irresistible. From Theodore’s ghost letter-writing job to some of the ways that Samantha attempts to inhabit his world, surrogates and artifices exist everywhere in the film. It is altogether interesting, exciting, depressing and frightening.

If this movie has a shortcoming, it is that there are almost too many ideas surfacing. Many movies suffer from a failure to deliver on their premise, where a cool idea often goes nowhere. This film had the opposite problem.

While I adored the first half, it ultimately saw things through too far and too explicitly. I might have been happier left to ponder some of the questions in a more open-ended way.

“Her” was certainly worth watching though and the performances were all wonderful. For an hour it was one of the best films I have seen in awhile.

But as in so many relationships, when the honeymoon phase ended, I was left slightly disappointed, somewhat disillusioned, but not at all sorry to have had the experience.