Well, they're back, and that sweet streak has grown like a cancer and killed any of the edge their humor may once have had. The early symptoms were visible in Shallow Hal, a film that briefly made fun of the overweight before making you feel bad for laughing. Now, with Stuck on You, they've made a paean to brotherhood that's almost all sentiment.
Here's a perfect example: A significant character in Stuck on You is retarded, and he's played by a similarly challenged actor named Ray "Rocket" Valliere. No jokes are made at this character's expense (by contrast, think of the way the retarded brother in Mary was portrayed), and the end credits include a clip of Valliere tearfully thanking the Farrellys and his costars for the opportunity.
Still, reducing the Farrellys' success to a bunch of retard jokes isn't exactly fair. Part of what made Dumb and Dumber and There's Something About Mary work was the way they took traditional premises -- the buddy movie and the romantic comedy -- and introduced weird narrative detours. Here, the narrative is a conventional Hollywood fantasy: Lovable small-town guy moves to L.A. to make it big, gets set up to fail, accidentally becomes a huge star, then learns that fame isn't all it's cracked up to be, meets the girl and realizes What's Really Important.
The sole twist in Stuck on You is that our protagonist is two people sharing one body, conjoined twins Bo (Matt Damon) and Walt (Greg Kinnear). An early plan to cast Woody Allen as Walt would have pushed the premise into true absurdity, but it isn't clear whether the Farrellys have that in them anymore.
The twins begin the film as fry cooks at a burger joint in Martha's Vineyard. But Walt feels driven to be an actor, and he wants to get to Hollywood before he's too old. He gets his big break when Cher, contractually forced to do a silly TV drama called Honey and the Beaze, spots the brothers and chooses Walt as her costar, assuming that his presence will cause the show to fail. Not surprisingly, the show becomes a huge hit.
If you've seen The Producers, you've seen this sort of thing done way better. I mean, really: What can you say about a comedy that resorts to the ancient gag of having a crying person borrow a silk handkerchief only to blow his nose into it loudly? You could say that the film's creators have lost it, and you'd probably be correct.