(Photo credit: Relativity Media)

"Don Jon" is Joseph Gordon-Levitt's debut as writer, director and star of his very own film, and for a guy who has both indie and blockbuster cred, the subject matter is extraordinarily risqué. Had it been done incorrectly, it may well have derailed this former child TV star's excellent career.

Good thing Mr. Gordon-Levitt did it right.

Gordon-Levitt plays Jon Martello, a studly Italian Jersey boy who tends bar, talks smack with his pals and beds a different girl every night. But his real passion is pleasuring himself while watching Internet porn. He's insatiable, something we learn as we're treated (mistreated?) to scenes of Jon enjoying himself to quick cuts of actual porn (or at least, the kind that's safe enough for an R-rated move). In Jon's mind, porn wins over actual sex every time. He's an addict but, of course, he doesn't think so.

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Jon, by the way, is meticulous, as addicted to keeping himself fit and his apartment neat and clean as he is to keeping the porn bookmarks on his Web browser organized. He also attends church regularly, where he confesses his sins - including his obsession with porn - and has regular dinners with his colorful family. Tony Danza plays his tough-talking, blue-collar dad; Glenne Headly is Jon's wistful mom who just wants her son to settle down; and Brie Larson is Jon's silent, always-listening-to-her-MP3-player younger sister, Monica, who we learn is actually paying a lot more attention to things than she appears to be.

So where's the conflict? Her name is Barbara Sugarman, played to sexy, manipulative perfection by Scarlett Johansson, who's also nailed the Jersey accent. Jon notices Barbara at his bar, but she isn't instantly consumed by his charms, as every other woman on planet New Jersey seems to be. Barbara makes out with Jon but refuses to go home with him and doesn't even give him her number.

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Jon is suddenly rendered average, but he's intrigued. He does what so many people do these days when they have amorous feelings toward a virtual stranger. He asks around, finds out who she is - and then stalks her on Facebook. Perfect.

The strategy works, but Barbara isn't giving it up anytime soon. Jon's going to have to work for it, which means he's going to have to develop feelings and fall prey to Barbara's anachronistic, over-the-top, smothering ideas about love. She wants to change everything about Jon. She even convinces him to go back to school to get a business degree, which is where Jon meets Julianne Moore's flaky Esther, a sexy older woman who may or may not change his myopic world view.

Oh, yeah, Jon is still addicted to porn, and that's going to be a problem.

Let's state the obvious: "Don Jon" is a most unconventional romantic comedy. What's not so obvious is it's also one of the most relevant romantic comedies you'll ever see. Gordon-Levitt delivers insightful social satire on love and relationships in a time when the Internet has birthed an era of unprecedented self-absorption and willingness to share personal information.

We already knew he was a great actor. With "Don Jon," Joseph Gordon-Levitt shows us he's also a promising director, and a talented writer with a knack for dialogue that's simple, yet smart and poetic. Well done.

Four out of five stars.

David Blaustein is the New York-based senior entertainment correspondent and film critic for ABC News Radio. Follow him on Twitter at @blaustein.