Dir: Adam McKay . US. 2008. 95 mins.

Playing like an overlong DVD version of one of his earlier, funnier, PG-13 films, the R-rated Step Brothers finds Will Ferrell diving into raunchier, coarser terrain, resulting in a movie that feels helplessly in thrall to its own foul language and sex jokes. Sporadically hilarious but as dim-witted and juvenile as its knuckle-headed title characters, Step Brothers seems to indicate that Ferrell and writer-director Adam McKay's partnership has lost some of its charm.

This Columbia Pictures offering, which opens in the US on July 25, has been smartly positioned between the June comedies Get Smart and You Don't Mess With The Zohan and August laughers The Pineapple Express and Tropic Thunder. Step Brothers marks the third time Will Ferrell and McKay have launched a summer comedy, the other two being solid hits: 2004's Anchorman ($85m domestically) and 2006's Talladega Nights ($148m). And Ferrell had been on a hot streak playing clueless, overgrown adolescents - until February's Semi-Pro, which was a major disappointment at $33.5m. So an interesting question underlying Step Brothers' release is whether that basketball spoof was an aberration or a sign of audience fatigue after a series of familiar roles. One also has to wonder if Step Brothers' R rating will cut significantly into Ferrell's teenage audience.

Whatever the case, Ferrell has a poor track record overseas, with his comedies usually bringing in more than 80% of their revenues in the States. It's difficult to imagine Step Brothers reversing that trend when the film starts rolling through international markets in August and September, but regardless, Ferrell should continue to score on ancillary.

Brennan (Ferrell) and Dale (John C. Reilly) are both 40, single, hopelessly immature and living at home when their single parents fall in love and get married, bringing the two men together under one roof. While these stepbrothers initially resent one another, they soon form a bond based on their shared childishness. But when their father (Richard Jenkins) demands that they grow up, find a job and move out, Brennan and Dale are thrown into the chaos of the adult world.

Step Brothers is unquestionably Ferrell and McKay's most professional-looking film together, ditching their previous comedies' rough-and-tumble edginess for a more conventional feel. But as if to compensate for this professional veneer, Step Brothers is almost unremittingly vulgar and crude, basing much of its humour on mentions (and one appearance) of male genitalia and a cast-wide volleying back and forth of a certain colourful four-letter word.

Although the film doesn't drag like Ferrell and McKay's previous outings, with their occasionally lumpy, improv-heavy scenes, Step Brothers' greatest liability is that, unlike those films, it doesn't have an inherently funny concept at its centre. Ostensibly a satire on family and modern man's fears of growing up, neither the characters nor the situation is clever enough to exploit that premise. The movie means to poke fun at the immaturity of its two characters, but the incessantly infantile comedy quickly feels like a concession to the baseness of its intended audience - a Dumb And Dumber for a new generation.

This is not to say that Step Brothers isn't extremely funny at times: With the film's rat-a-tat style of jokes, it would be impossible for a few not to hit their target. Neither Ferrell nor Reilly has a solid character to play - they're essentially two versions of the same idiot. But Ferrell's lunatic mania does allow for some great moments, while Reilly's vulnerability makes his Dale a likable boob.

Production companies

Relativity Media

Apatow Productions

Mosaic Media Group

Gary Sanchez Productions

Domestic distribution

Columbia Pictures

International distribution

SPRI

Producers

Jimmy Miller

Judd Apatow

Screenplay

Will Ferrell

Adam McKay

(story by Will Ferrell & Adam McKay & John C. Reilly)

Cinematographer

Oliver Wood

Main cast:

Will Ferrell

John C. Reilly

Richard Jenkins

Mary Steenburgen

Adam Scott

Kathryn Hahn

Andrea Savage

Rob Riggle