“Blue is the Warmest Color” opens Friday at Sundance Cinemas. Not rated, 2:55, three and a half stars out of four.

“Blue is the Warmest Color” is a beautifully imperfect film about a beautifully imperfect love affair. Abdellatif Kechiche’s Cannes Film Festival winner has been on the receiving end of both rapturous praise and brutal criticism since it premiered in May — either it’s the best French love story since “Breathless” or it’s anti-feminist pornography masquerading as an arthouse epic. I’ve wrestled with both extremes in the few days since I’ve seen it, and I’m wrestling still. But I know there are moments of great tenderness and artistry here, especially in the performance, that make me think the missteps were at least honorably made.

Adele (Adele Exarchopoulos) seems like a typical French teenager, hanging out with her friends, interested in creative writing, sexually curious but inexperienced. Her more experienced friends are pressuring her to lose her virginity, but when she does find a perfectly nice boy, the experience is strangely unsatisfying.

One day on the street, her eye catches that of a blue-haired older girl, an art student named Emma (Lea Seydoux). It’s a fleeting moment, but one that Adele can’t shake. Weeks later, when she finds herself in a lesbian bar accidentally on purpose, she sees Emma, and strikes up a conversation. That conversation turns to attraction, that attraction turns to lust, that lust to turns to love.

That description moves pretty briskly through what is a rather leisurely first half. Kechiche gives Exarchopoulos and Seydoux lots of space to breathe and inhabit their characters. It makes for a film that’s slow going for a while; Adele’s teenage life so ordinary that one wonder why we’re seeing so much of it. But those small, offhand moments add up into a convincingly complex portrait of an aimless teenager, and when Adele finally connects with Emma, there’s a real force behind that collision.

And then there’s the sex. The scenes that earn the film its NC-17 rating have been very polarizing to viewers, and seem deliberately provocative on Kechiche’s part. What’s really striking about them isn’t so much how explicit they are, but how long they are. We’re used to seeing sex scenes of a minute or two at most — the first scene between Adele and Emma runs over 10 minutes. Since we don’t see scenes that long outside of pornography, many conclude that makes this pornography. And there are moments within that they do feel a little tawdry, where the cameras seem to be gazing at two pretty naked bodies coupling from a distance, rather than inhabiting the two complex characters we’ve come to know in the film.

But on balance, the scenes are going for something deeper than titillation. They aim to draw an explicit connection between sex and love, between the giving and receiving of pleasure and the exchange of emotions, that’s very rare in films. And those 10 minutes can really be understood only in the context of the entire three-hour film, in particular what happens in another 10-minute scene that happens late in the film.

The second half of “Blue is the Warmest Color” moves forward a few years in the relationship. Adele and Emma are living together; Emma is an up-and-coming artist on the Paris scene, while Adele is a kindergarten teacher. The sex is still great, and they care for each other,but their differences, mostly revolving around class and ambition, are starting to widen. At a party for Emma’s artist friends, Adele is treated as sort of the dutiful housewife, the one who serves and cleans up while Emma and her friends chat about art and politics.

It’s this second half of the film that really proves its mettle, how insightfully Kechiche charts the maturing and settling of a long-term relationship, how compromises and small grievances eat away at the seeming perfection of a love affair’s beginning. Seydoux and Exarchopoulos are just so raw and fearless together, generating an intense, crackling chemistry for Adele and Emma at their best and worst. Theirs is a love story that, flaws and all, you won’t soon forget.