Tracy Letts made his name with an act of one-upmanship: August: Osage County, which earned Letts both a Pulitzer and a Tony, is the dysfunctional family drama to end them all, an emotionally draining three-hour opus that draws upon Faulkner, Williams, O'Neill, Albee and Shepard. Letts throws all his predecessors' most lunatic characters into a sweltering three-story manse and lets them gnaw one another into submission; it is not better than Cat on a Hot Tin Roof or Long Day's Journey Into Night, but it is louder and meaner, and it is impossible to imagine anyone trying to top it. With August, Letts declared an entire genre of American dramatic literature finished, roaring, "I'm in charge now!"

His follow-up, which plays through Feb. 12 at Artists Repertory Theatre, is less noisily ambitious. Superior Donuts is an odd-couple comedy of familiar form: Arthur Przybyszewski, a burnt-out, emotionally stunted former radical and draft-dodger who now runs the Chicago donut shop his father founded, hires Franco Wicks, an exuberant, uninhibited black 21-year-old with dreams of literary stardom, to work the counter. They banter, hilariously, as Franco tries to draw his reticent boss out of his shell, bluntly appraises his appearance ("Let me tell you who looks good in a ponytail: Girls. And ponies.") and proposes he add poetry readings ("Poets can't pay the rent, but they drink coffee like a motherfucker").

It's a comfortable, entertaining, even heart-warming character comedy, directed without fireworks by Allen Nause. Bill Geisslinger, who last appeared at Artists Rep as the burnt-out middle-aged cynic Sharkey in the company's 2009 production of The Seafarer, incorporates some of that character into Arthur, by way of The Dude and maybe Harvey Pekar. Vin Shambry, a veteran of New York productions of Hair and Rent with few nonmusical credits in his bio, is immediately likeable as Franco. He is constantly in motion and endlessly curious, part grifter, part eager student. We love him as soon as we see him.

Letts knows this and, because he's an emotional terrorist, abruptly saddles Wicks with implausible gambling debts, collected by a pair of anachronistic Irish thugs borrowed straight from 1970s Mamet, and sends the plot spinning off into unearned tragedy. It's a silly, self-indulgent move, and brings with it enough stupidity—some really offensive Russian stereotypes, a badly choreographed fight scene and body horror that will come as no surprise to anyone who's seen Artists Rep's ads for the show—to nearly sink the ship. Most of the second act is disappointing, but Shambry and Geisslinger build up a strong enough head of steam in the first that even the final scene, a blunt allusion to The Cherry Orchard, cannot completely overwhelm my good feelings about the show. Adjust your expectations accordingly.