Comedy being notoriously subjective, I can't just up and say, "Role Models is really funny and for that reason you should go see it," even though it is really funny, and you should go see it. Fortunately, there is a lazy yardstick I can use: if you, like me, think that Paul Rudd is one of the modern cinema's great under-appreciated funnymen, then you, like me, will enjoy Role Models, although not to such an outlandish degree that you should get your hopes up for the best comedy of the year, or something like that.

Reteaming Rudd with David Wain, director of Wet Hot American Summer and The Ten, the new film is about two thirtysomething coworkers, misanthrope Danny (Rudd) and cheerful horndog Wheeler (Seann William Scott), whose job driving from school to school selling kids on a bright green energy drink named Minotaur is driving Danny into an intractable depression. Throw in his break-up from his girlfriend of seven years, Beth (Elizabeth Banks), and it's not so hard to believe that he might do something a little bit drastic - the sort of drastic that results in the choice between 30 days in jail or 150 hours of community service.

The community service that the two men are assigned is an outreach program teaming troubled, lonely kids and grown-up mentors called Sturdy Wings, founded by the deranged ex-crackhead Gayle Sweeny (Jane Lynch). Recognising that Danny and Wheeler haven't any choice in the matter, she assigns them two of the hardest cases in her books: Wheeler is teamed up with the foul-mouthed, sex-obsessed Ronnie (Bobb'e J. Thompson), while Danny is given to the much-too-old Augie (Christopher Mintz-Plasse), a LARP enthusiast who doesn't understand why people make such a deal about having friends in real life. If you expect this to end with all four boys learning lessons about being men, and forming bonds that will last forever, you get a bright, shiny cookie.

As the first unabashedly mainstream project for indie-comedy god Wain (whose work also includes the cult-beloved TV shows The State, Stella and the current Wainy Days), Role Models could easily have been a great deal worse than it is. Modern history is littered with the bodies of aggressively quirky comic minds whose personalities can't make the transition to audience-friendly work (something that Paul Rudd knows a bit about, in fact), but it seems to be a reasonably comfortable fit for Wain - Role Models is hardly as creative as his best work, but it's at least a significant improvement over his last feature, the muddled sketch-comedy The Ten.

The best part about the film is its small scale: in an environment where most mainstream comedies strain to make their jokes as zany and crazy as possible, with outlandish slapstick and impossible malapropisms scattered across the landscape like trenches in the Somme, Role Models has the unspeakable bravery to base almost all of its comedy on things that could actually happen. There are broad swipes here and there, but in the main, this is an appealingly human-sized comedy: it is entirely reasonable that Danny would act like he does in the opening scenes and that this would lead to his altercation which kick-starts the film; it is more than reasonable that two men with no criminal records would be assigned to a Big Brother program for what it is ultimately a victimless crime; and most of the things that happen with the kids are within the realm of believability, though they are undoubtedly contrived. The one character who just wouldn't work in the real world is happily played by Jane Lynch, a crackerjack comic performer who is never ever going to get the recognition she deserves, and who brings to her character in this film a twitchy intensity that makes her seem even scarier as a friend to children than she would have as a drug addict.

(By the way, I'm not trying to argue that realistic comedy is always better than zany comedy, of course, but it's certainly better than zany comedy done as badly as it has been for most of this decade).

As long as the film confines itself to character-based comedy, it does pretty well for itself: Rudd is a delight as always, and Seann William Scott continues his gentle trajectory from irritating goofball to genuinely effective comic actor, and their chemistry together is quite good, as is their timing. The problems creep in when the writers - including Wain and Rudd, and fellow State alum Ken Marino - try to do something with that edgy sex comedy that everyone's talking about (and which worked so well for Wain in Wet Hot American Summer. Acknowledging that tastes vary, and everyone in the theater where I saw the film seemed to love this stuff, the fratty humor just plain didn't work for me in this case, particularly in the character of Ronnie, who seems to have been written according to the theory that watching a 9-year-old black boy say "boobies" is ipso facto hilarious. It's through no fault of the young actors, both of whom do well and seem personally charismatic, that Ronnie and Augie aren't that interesting or appealing as characters - they're saddled with the plottiest bits of the film when they aren't given its worst gags.

Besides that, Wain proves himself to be a better director of comedy than a director of movies. Except in Wet Hot, with its note-perfect evocation of early-'80s sex comedies, he's never seemed to attend all that much to how his films look, nor really how they're paced, and Role Models has plenty of slow stretches, although atypically it's not "a slow stretch in the middle" or "at the end" - more like a whole lot of scenes that go on half again too long, or shouldn't be there in the first place, all through the movie. Though (perhaps surprisingly) the film earns its tied-up-with-a-bow ending, it takes a few too many false crises to get us there.

Even if it's no masterpiece, though, Role Models is funny - and that's huge for a movie in this day and age. Looking at its carefully unchallenging framework, I find myself wondering if this is a case of a film that's no worse than it needs to be - Wain's sensibility watered down is obviously less interesting than Wain unfettered, but this is still a far cry from the worst of modern R-rated comedy. It's hard to dislike, and that means by default that it's hard to love, but I can't be too hard on something that made me laugh.