Of the three films that writer-director Adam McKay and writer-actor Will Ferrell have collaborated on, "Step Brother" is an ever-so-small step forward from 2004's "Anchorman: The Legend of Ron Burgundy" and 2006's "Talladega Nights: The Ballad of Ricky Bobby." All of them have sparks of an interesting idea, but are ultimately done in by a pedestrian script that earns a few belly laughs, but twice as many groans. Narrative momentum is off on all of the above, too; their plots just sort of mosey around, searching for a point until the feel-good ending. With the affable, quasi-bizarre "Step Brothers," at least it actually earns that conclusion.

Brennan Huff (Will Ferrell) and Dale Doback (John C. Reilly) are unemployed 40-year-olds still living at home with their single parents—Brennan with patient mom Nancy (Mary Steenburgen) and Dale with harried physician dad Robert (Richard Jenkins). When Nancy and Robert lock eyes at a convention, it is love at first sight. Once married, Nancy naturally moves in with her new husband, and with her comes a largely displeased Brennan, forced to share Dale's bedroom with him. These two grown children clash at the onset, but soon come to find they make a pretty good team when Dale punches out Brennan's snooty, younger career brother Derek (Adam Scott). When the stress of having to share a roof with kids who should have long since left the nest ends up putting a strain on Nancy's and Robert's relationship, it is up to Brennan and Dale to finally take charge of their futures and grow up once and for all.

The hostility between Brennan and Dale in the first half-hour of "Step Brothers" is unpleasant bordering on painful, like nails on a chalkboard or silverware being scraped together. It's not enjoyable watching them fight and destroy the house, but then director Adam McKay actually curves away from expectations and allows these two to find a common ground. Once they have become tight friends, the film improves considerably. Still, there are many dry spots where the gags fall flat—Brennan's and Dale's simultaneous sleepwalking incident is horridly unfunny, for example, and a raunchy sequence in which Brennan graphically rubs his balls all over Dale's drum set feels about a decade too late—and the pacing doesn't really escalate so much as it simply wanders from one episodic set-piece to the next. Why is it, also, that Brennan and Dale act like average, albeit directionless, men some of the time, and then resort to such childish actions and mannerisms that they almost seem mentally handicapped? With a few tweaks, the picture could have actually been about 12-year-old step-brothers, and been better for it.

Uneven to say the least, "Step Brothers" is really quite strange in the way it is so over-the-top that it approaches slapstick, but then also provides moments of sincerity (a lot of them involving marital troubles between Nancy and Robert) and pitch-black, "War of the Roses"-style comedy (Dale starts to bury Brennan in the backyard when he accidentally knocks him out and believes him to be dead). The unabashed silliness is good for a handful of amusing scenes, as when the controlling Derek forces his almost robotic family to join him in a car sing-along to Guns N' Roses' "Sweet Child O' Mine," or when Derek's unhappy wife Alice (Kathryn Hahn) comes onto Dale in a public bathroom. After about twenty seconds of sloppy impromptu sex, Alice happily proclaims, "That was exactly how I imagined it." When Brennan sings in front of Dale, Dale has a great zinger: "Your voice is like a cross between Fergie and Jesus."

The natural camaraderie that Will Ferrell (2008's "Semi-Pro") and John C. Reilly (2007's "Walk Hard: The Dewey Cox Story") share makes the material much more palatable than it otherwise might have been. Both have the potential for greatness, and character actor Reilly has recently found a new calling in the world of comedies. Even when their characters of Brennan and Dale are acting stubborn or immature, they're somehow likable. As parents Nancy and Robert, Mary Steenburgen (2007's "The Brave One") and Richard Jenkins (2007's "The Kingdom") get good parts at opposite ends of the spectrum. Whereas Nancy finds herself nurturing Brennan even when he's difficult, Robert's end-of-his-rope abrasiveness is only a temporary front for how much he truly cares and worries about Dale. He wants his son to move on with his life, and his last option is the tough love treatment. In a remarkably uninhibited supporting turn, Kathryn Hahn (2007's "The Last Mimzy") is a colorful hoot as Alice, a married woman who can't control her attraction to Dale.

If writer-director Adam McKay and co-writer Will Ferrell really wanted to make a movie that touches on twenty-five-year-long adolescence, they haven't done that. Truths emerge every now and again, such as the sibling rivalry between Derek and Brennan, but the film doesn't stay focused long enough to say anything of note about it. "Step Brothers" is not without its fleeting pleasures—the first arrives before the opening frame, with a typically asinine quotation from George W. Bush about family—though it can't be denied that a tougher, more organized and consistently funny picture on the same subject could have been produced with a little more work done on the screenplay level. It's a close call, but the film comes up about a millimeter short.