I don't want to oversell "The Rocker," but in a summer of erratic, assaultive comedies all up and down the budget scale, this Rainn Wilson vehicle—a kind of "Home School of Rock"—stakes out its own corner of the market. It's a lot of fun. Its spirit is genuine and, even with the odd vomit gag, fundamentally sweet.

Wilson's mug, dominated by a significant expanse of Van Heflin forehead, is famous thanks to " The Office," on which Wilson plays paper pusher Dwight Schrute. The actor has registered strongly in movies as well, notably as the convenience store clerk in "Juno." Directed by Peter Cattaneo, who brought a working-class edge to "The Full Monty," "The Rocker" allows Wilson a chance to play to his strengths and dine out on a wild-eyed dork.

Back in the 1980s, Robert "Fish" Fishman, thrashed the drums for a rising hair band called Vesuvius. Just before the band hit it big, Fish was bounced. Cut to the present: Fish lives, bitterly and in a state of perpetual ax-grinding, with his sister (Jane Lynch), her husband (Jeff Garlin) and their teenage son Matt (Josh Gad). Matt's in a band. The band loses its drummer; Fish steps in, eagerly, hitting the road with the kids.

Here's an example of where "The Rocker" goes right. Matt is a plus-size kid with zero social skills, counterbalancing his charismatic young band mates Curtis (Teddy Geiger) and Amelia (Emma Stone, of "Superbad"). But Gad works in a lower key than Jonah Hill in "Superbad"; each sleepy-eyed utterance arrives slightly behind schedule, so that even standard-issue dinner-table trash talk directed at his sister—"If you don't stop annoying me, I'm going to shave your head in your sleep"—sounds like a real teenager talking, rather than a Neil Simon alum "delivering."

The script, spiced with stranger and fresher pop-cult references ("Miss Saigon," anyone?) than the norm, is by Maya Forbes and Wally Wolodarsky, whose credits together and separately include "The Larry Sanders Show," "The Tracey Ullman Show" and " The Simpsons." Anthony B. Richmond's cinematography whizzes straight past Midwestern ordinariness to flat-out unsightly, but director Cattaneo keeps the tone steady and the mugging to a minimum. Do you buy the romance between Fish and Curtis' mom (Christina Applegate)? Not really. Is Wilson a memorable physical comedian? Not yet: At this point, he's all face and voice. But he's a real actor. And he doesn't look like anyone else on the planet, which never hurt anyone.

See the trailer and find local showtimes for "The Rocker."