In “This Is 40” Judd Apatow attempts, as he did in “Funny People,” a more serious treatment of family relationships than in his early films—though still in a comedic vein, of course—but in the end it doesn’t manage to go much deeper than they did. Moreover, it’s still as coarse as we’ve come to expect of him, and though it improves in the last act, it also becomes less edgy and more conventional there. The result is only fitfully amusing and overall rather irritatingly self-absorbed—Apatow navel-gazing and posting the result for our dubious benefit.

The script focuses on the secondary couple from Apatow’s smash “Knocked Up”—Pete (Paul Rudd) and Debbie (Leslie Mann). It’s some years on from the earlier picture—both are on the cusp of their forties, as the title indicates—and Paul’s opened up a “nostalgic” record label while Debbie’s running a boutique. Neither business, it must be said, is thriving, yet the couple still live in pretty high suburban style along with their two daughters, moody teen Sadie (Maude Apatow) and her eight-year old sister Charlotte (Iris Apatow).

You’re intended to believe that this family loves one another deeply, but they spend most of their time bickering and screaming; it’s a very noisy household. Bubbling beneath the surface are the monetary problems—Pete’s signing of old-timer Graham Parker quickly becomes a bust, and Debbie’s faced with the suspicion that one of her clerks, sultry Desi (Megan Fox), has been embezzling from the store. Meanwhile they’re both stressed by encroaching middle-age, and by the demands of parenthood. Sadie’s addicted not only to Facebook, where a fellow student is posting mean messages about her, but to the TV series “Lost,” which she’s watching episode by episode enthralled. And she’s constantly at loggerheads with Charlotte, who of course is wise beyond her years. (At one point she even acts as the voice of reason, reflecting the viewer’s feeling by saying that she’s tired of all the fighting.) The family seems, in fact, on the verge of breaking down, until it reaches a fresh start in the events surrounding Debbie’s big birthday party.

Even before that, it should be noted, there are oases of mirth amid the generally unpleasant din of the family squabbles—which are marked, unhappily, by a stream of offhandedly foul language and an impressive collection of sexually gross moments. Many are provided by Albert Brooks as Pete’s dad, who’s remarried and is sponging off his son, who can’t afford it. Brooks does his laid-back nebbishy, self-deprecatory routine so well that you can’t help but smile every time he appears to recite the droll dialogue either Apatow or he has come up with. There’s some funny stuff, too, in Pete’s music-business business, especially the harangues of his assistant (Chris O’Dowd) and the quiet resignation of Parker. But Apatow goes too often for the comic jugular in his usual style—as in a couple of scenes involving Catherine (Melissa McCarthy), the bellicose mother of that Facebook-posting classmate of Sadie’s, which extract laughs from profanity-laden bellowing. Apatow likes one of them so much that he includes an extended version of it in the closing credits—and audiences who wallow in such stuff will love it, too. But it’s really humor at the lowest of brows. And the material focusing on Debbie’s other clerk, Jodi (Charlyne Yi), is so strange that it seems to come from another movie entirely.

A measure of redemption occurs, in every sense, in that last-act birthday party, when Brooks pops up again and is joined by John Lithgow as Debbie’s distant, fastidious dad, who’s a perfect counterpoint. Together these two old pros give a master lesson in timing and restraint—something the rest of the company might have learned from. Unfortunately, Apatow opts for more raucous goings-on to end things on a “high” note rather than following their lead.

Rudd and Mann certainly inhabit their roles as a couple struggling to find some sort of balance in their lives, but they tend to overdo their big moments—more a function of the writing than their failing as actors—and the Apatow kids similarly tend toward the manic. O’Dowd’s overplaying works better, in the pure sitcom sense, and though she’s stuck with a rather unseemly character twist, Fox comes across as surprisingly likable. Jason Segel also has a pleasant cameo, and Yi does what’s asked of her—which is nothing worth watching. (Unless I missed it, there’s no reference as to why Seth Rogen and Katherine Heigl’s Ben and Alison around heard from this time around.)

As usual in Apatow product, the technical credits are professional, though the faux-realist approach of cinematographer Phedon Papamichael, accentuated by the editing of Brent White and Jay Dauby, tries to invest the material with a dramatic credibility it really doesn’t warrant. There’s a great deal of emphasis throughout on pop music (including lots old tunes chosen by supervisor Jonathan Karp), which is defensible on plot terms given Pete’s current occupation, but is really another of the writer-director’s characteristic crutches, using shared memories with his audience to do his dramatic work for him. It saves him the need to pen truly revealing dialogue.

Though it’s about the encroachment of middle-age, “This Is 40” doesn’t really represent much of an advance in Apatow’s fundamentally adolescent attitudes. That may sit well with his fans, but it’s beginning to appear to be a case of arrested cinematic development.