If you loved “Forgetting Sarah Marshall,” you might find this overlong, which reunites that movie’s producer, writer, director and star, enjoyable. But you might still feel the absence of Russell Brand, who for most of us was the earlier movie’s saving grace. He’s replaced here by two substitutes—Chris Pratt as the man’s loudmouth chum and Alison Brie as the woman’s spacey sister, who wind up as a secondary couple in the script—but they’re not sufficient compensation.

You may also find that the movie lacks a credible core and tries much too hard to make certain that every moment is crammed to the full with some goofy, often vulgar, joke or gag. The premise is that Tom Solomon (Jason Segel, who also co-wrote the script with director Nicholas Stoller), a sous chef at a ritzy San Francisco restaurant, pops the question to recent psychology PhD Violet Barnes (Emily Blunt) on New Year’s Eve after a one-year relationship. They happily begin planning the wedding, including an engagement party at which his garrulous best buddy Alex (Pratt) and her sister Suzie (Brie) make embarrassing toasts—as well as shacking up afterward, with predictable results that necessitate their getting hitched speedily.

Meanwhile Violet gets an offer of a post-doc at the University of Michigan, which leads good-hearted Tom to give up his job and move with her to Ann Arbor for an expected two years, during which they’ll postpone the wedding. Unfortunately, the only job Tom can find is one for which he’s completely overqualified—as a clerk in a sandwich shop. And since Violet’s is pretty much monopolized by her faculty mentor, smooth operator Winton (Rhys Ifans), and her fellow post-docs—a weird band consisting of firebrand Doug (Kevin Hart), dippy Vaneetha (Mindy Kaling) and oddball Ming (Randall Park)—he gravitates into a friendship with another faculty husband, Bill (Chris Parnell), a goofy guy who spends his days knitting sweaters and introduces Tom to the joy of deer hunting (involving, intentionally one hopes, some of the worst phony animals in the history of the medium).

When Winton comes on to Violet—and she’s offered a five-year extension of her post-doc and eventually a tenure-track assistant professorship—it’s entirely predictable that Tom and she will break up; she winds up with Winton and he, back in San Francisco, at Alex’s restaurant with a young coed in tow (unless I missed it, we’re never told how they got together). Of course the separation is only temporary. The rules of this genre require that such a story wind up with a wedding, however long it’s been postponed, and expectations aren’t disappointed in this case.

The basic problem with all this is that the screenplay’s emphasis on a wedding ceremony comes across as completely old-fashioned. Tom and Violet have apparently been living together even before he proposes, and they share a house in Michigan—and are intimate there. It’s not as though the lack of a certificate has had any real effect on their relationship. In old Hollywood screwball comedies that might have been a serious impediment to happiness (or social acceptance), but nowadays it all seems much ado about nothing, and so merely a pretext for the jokes.

And many of those are in pretty poor taste, as is contemporary custom in such fare. Ticking off the delay of the ceremony with periodic inserts of the funerals of Violet’s grandparents, for example, must have sounded more amusing on paper than it turns out to be on the screen. Segel bares his derriere so frequently that you’d think he’d gone into competition with Will Ferrell in that regard. (He seems also to love prolonged scenes of lusty screwing around in bed.) Michiganders, especially those in the fairly sophisticated college city of Ann Arbor, might well resent being portrayed as such backwoods buffoons, and the whole field of behavioral psychology is treated as little more than slapstick nonsense. There’s also less humor in the loss of digits, either through knife cuts or frostbites, than is expected here. (That also leads to a continuity flaw, when one character slices off her finger early on but is later shown with the hand perfectly fine.) And saucy sex talk is dropped into the mix constantly for cheap laughs.

Stoller encourages his cast to go all out for the laughs. Segel certainly leaves nothing to the imagination, whether it be baring his butt or sporting a handlebar moustache, and Pratt launches into the role of resident jerk with almost unseemly brio. Hart, Kaling and Park similarly go for broke, and though Brie settles down some after a wild-eyed beginning. There’s little room for subtlety here, but Ifans smoothly covers the part of a scoundrel. Blunt, however, never quite gets into the scheme of things. She appears a mite uncomfortable much of the time, as though she were barely in on the joke. She seemed much more at home in “Salmon Fishing in the Yemen.”

As befits a sausage from the Apatow factory, “The Five-Year Engagement” is smoothly produced, except for some patently phony cold-weather scenes (made all the more obvious by comparison to inserts shot in an authentic Michigan winter). Javier Aguirresarobe’s cinematography is fine, and all the other technical contributions are professional. Though the two-hour plus running-time is excessive, even the editing by William Kerr and Peck Prior can’t really be faulted; they keep things moving at a quick clip—it’s just that they had too many things to squeeze into the finished package.

Back in 2004 Jean-Pierre Jeunet made a film called “A Very Long Engagement”—a wartime epic with a lovely streak of genuine romance. If you want to see a picture about a protracted engagement, that’s the one to opt for, rather than this crude, disjointed, overextended and only sporadically funny effort.