Carrying decades of bottled-up rage, Pearl isn’t an easy woman to romance, and she’s an impossible mother. Her overweight, divorced daughter, Bibby (Kathy Bates), feels flayed by her mother’s sharp tongue. Her other divorced daughter, Norma (Marcia Gay Harden), has retreated into fantasy after the death of her younger child. From one day to the next, she’s likely to appear as Marilyn Monroe, Jackie O or Mrs. Robinson in “The Graduate.” Norma’s neglected 12-year-old son (Matthew Branton) may have inherited his mother’s craziness: convinced he’s invulnerable, he keeps hurling himself into danger.

“Used People” takes a traditional romantic comic form and infuses it with a fresh, crowded sense of community. This mixture of old and new (reminiscent of “Moonstruck” in its risky mood swings) is reflected in the multigenerational talent who made the movie. The great veterans on screen, such as Jessica Tandy and Sylvia Sidney, are masterfully directed by the 31-year-old Englishwoman Beeban Kidron, who treads an artful line between fantasy and reality, sentiment and sentimentality: pain and charm. And the witty, richly inventive screenplay is the work of 33-year-old actor/writer Todd Graff. From Rachel Portman’s entrancing score to Stuart Wurtzel’s magically shabby production design, everyone involved seems keyed to the same delicately skewed wavelength. But it is Mastroianni and MacLaine who send the movie soaring. What other actor but the effortlessly enchanting Mastroianni could make one believe in this improbable white-suited knight? And MacLaine, always at her best in roles that tap into deep-seated anger, gives one of her finest performances. Her Pearl is cruel, appalling and wonderful; when this wary widow breaks out of her shell and smiles, she seems lit from within. By the end of “Used People,” we’re looking at her, and the world, through Joe’s moonstruck eyes.