“Meet the Parents” (2000) was a lowbrow but fitfully funny comedy about mismatched prospective in-laws; the sequel, “Meet the Fockers” (2004) was a gross, smarmy expansion on the theme, which ratcheted up the level of raunchiness and sexual innuendo. But it was a smash, so it’s not surprising it’s spawned another sequel. While not as obnoxious as its predecessor, “Little Fockers” an uninspired riff on an old formula, and structurally a shambles; and though Jay Roach has ceded directorial duty to Paul Weitz, an experienced comic helmer, it’s clumsier and sloppier as well.

As the title suggests, involves the next generation, Samantha and Henry (Daisy Tahan and Colin Baiocchi), the five-year old twins of doofus nurse Greg Focker (Ben Stiller) and his wife Pam (Teri Polo). But the emphasis is still on Greg’s difficult relationship with his father-in-law Jack Byrnes (Robert De Niro), a control-freak ex-CIA agent who, suddenly conscious of his mortality when he has a heart attack, decides to anoint his son-in-law the new head of the family. And Greg will have to prove his worth by making more money, fixing up a perfect homestead and securing a fine education for the kids—things Jack will scrutinize when he and his wife Dina (Blythe Danner) visit for the children’s fifth birthday party. There will be other guests, too: Kevin (Owen Wilson), the oddball ex-suitor of Pam whom Jack still prefers to Greg, and Greg’s hedonistic parents Bernie (Dustin Hoffman), who’s abruptly traveled to Spain to study flamenco dance, and Roz (Barbra Streisand), a TV host who specializes in conversation about sex.

Even setting aside one big continuity issue—in the first movie Pam had a brother named Denny (Jon Abrahams), who would undoubtedly be Jack’s first choice as family head had he not unaccountably disappeared—the script of this picture is a mess, a jerry-rigged construction that’s more a collection of poorly-written sketches than a coherent whole. There are scenes in which Greg gets involved with an aggressively chipper (and unaccountably lascivious) pharmaceutical rep named Andi (Jessica Alba), and others set at a “progressive” school run by Prudence (Laura Dern). There are a couple of sequences involving a shady contractor (Harvey Keitel) who’s taking Greg for a ride on his house renovations. There’s a weird birthday-party episode in which Wilson totally embarrasses himself doing a strange gymnastic routine (and follows it up with an even more embarrassing tete-a-tete with Streisand). And what to make of the stuff involving the grinning Hoffman and his obsession with flamenco, which come completely out of left field? All these bits are poorly constructed—lots of set-ups without payoffs, and some payoffs that are prolonged beyond endurance—and directly, surprisingly slackly, by Weitz, who’s timing seems totally off.

Of course, the center of the movie remains the tense relationship between Greg and Jack, which has grown more and more unfunny over time. In this case there’s less gross-out comedy than in the second picture, but the makers make up for the diminished quantity with extremely low quality, especially in an erectile-dysfunction sequence between the duo that’s really excruciating to watch. (These “four-hour erection” sequences are becoming one of the most tiresome cliches in what passes for comedy in Hollywood nowadays.)

Under the circumstances it’s understandable that the cast just seem to be going through the motions, except from Alba, who overdoes the enthusiasm to such an extent that she seems totally spaced-out. Stiller and De Niro slog through the plot without conviction, but surely it’s Hoffman and Wilson who must endure the greatest indignities. They might consider replacing their agents, though presumably the fat paychecks will provide some solace from the inevitable critical brickbats.

“Little Fockers” is garishly shot by Remi Adefarasin, and no fewer than three editors—Greg Hayden, Leslie Jones and Myron Karstein—handled the chore of trying to assemble the footage smoothly, unfortunately without much luck (they insert lots of Chicago exteriors to establish the locale, but the picture was clearly shot elsewhere—the suburban streets, in particular, are suspiciously vacant). Stephen Trask’s score is anonymously jaunty.

“Little Fockers” ends up virtually promising another sequel. Or is that a threat?