Mark Ruffalo has repeatedly demonstrated his on-screen credentials, but even the best actors can benefit from a strong directorial hand. “Infinitely Polar Bear,” in which he plays a manic-depressive (or bipolar man, of which the title is his own childishly mangled version) who takes on the responsibility of caring for his two daughters while his wife is away at school, was, however, helmed by first-timer Maya Forbes. Her neophyte status might have been a problem in itself, but her emotional connection to the material—based on her autobiographical screenplay—perhaps prevented her from reining in the man who was standing in for her deceased father. In any event as Cameron Stuart, the fictionalized version of her dad, Ruffalo gives the sort of oversized, flashy performance that calls too much attention to itself for the film’s good. Still, the result will undoubtedly appeal to viewers happy to accept a feel-good account of events that in real life probably had a far more ambiguous quality than the one depicted here.

The story is a relatively simple one. After suffering a breakdown in 1978, Cameron is taken away for treatment by the state of Massachusetts, and his wife Maggie (Zoe Saldana) effectively becomes a single mother to their daughters Amelia (Imogene Wolodarsky, the daughter of Forbes and producer Wally Wolodarsky) and Faith (Ashley Aufderheide) in Boston. Cam improves under medication and is eventually released, but continues to live apart from the family, though the relationship among the four remains strong.

Since they receive only minimal support from Cam’s family—all are dependent on carefully-calibrated disbursements from a trust controlled by his grandmother (Muriel Gould)—Maggie looks for ways to earn more money, and wins a scholarship to the Columbia Business School’s MBA program. So she suggests that Cam take over the rearing of the kids in Boston for the next eighteen months, while she studies in New York, returning to Boston over the weekends. And anxious to become a full-fledged member of the family unit again, he agrees, though both he and his parents—played in an amusing one-scene cameo by Beth Dixon and Keir Dullea—have serious reservations about whether he can handle the responsibility.

From this point “Infinitely Polar Bear” becomes a serio-comic take on the “Mr. Mom” template, though the girls are older and the dad no mere bumbler but a man with a serious underlying personality disorder. Forbes’ script doesn’t entirely skirt the darker side of the equation: especially in Cam’s early days as bachelor father, as it were, his ability to maintain his balance while keeping the apartment tidy and seeing to the girls’ needs is shaky, and his attempts to ingratiate himself with the neighbors come across as so aggressive that they’re off-putting. But even when he leaves the girls alone in bed to go off for a long night at a bar, Forbes treats it as a mild misdemeanor. She also dismisses his drinking, smoking and reluctance to stay on his meds as minor matters. Instead she emphasizes his vitality and charm as he grows ever closer to his daughters and overcomes the obstacles they face, even in unorthodox ways. In the process Forbes understandably turns the screen version of her father into less a troubled soul than an endearing eccentric.

Ruffalo falls in with this perspective on the character. There are a few instances—in the frantic breakup scene at the start, during a sequence in which he explodes when his daughters prove obstreperous when he asks them to set the table, in another as he confronts a friend about not giving his wife a job—when he embraces Cam’s demons and shows them operating in full force. Overall, however, he presents the man as excessively exuberant, but so lovable and anxious to please that even when he’s drinking or off his meds, nobody need be concerned about his depressive side erupting and endangering his children. And Ruffalo rarely resorts to subtlety in making the point. The result is the sort of florid, highly histrionic turn that resembles the one George C. Scott gave back in 1971’s “They Might Be Giants.” You can enjoy watching it, but probably won’t find it less than credible. Wolodarsky and Aufderheide are extremely exuberant too, but beside Ruffalo they come across as relatively subdued, while he casts Saldana completely in the shade. This is a modestly budgeted picture, but the technical contributions are fine, with the period detail nicely captured in Carl Sprague’s production design, Jennifer Engel’s set decoration (especially in the Stuart’s cluttered apartment) and Kasia Walicka-Maimone’s costumes, and Bobby Bukowski’s cinematography and Michael R. Miller’s editing giving the action, which clocks in at a brisk 87 minutes, energy and flow.

Forbes’ film undoubtedly looks back on her adolescent experience through rose-colored glasses, and draws from Ruffalo the sort of gleefully over-the-top performance that’s actorish in the highest degree. But it anchors a picture on a potentially difficult subject that instead is content to be a manipulative crowd-pleaser, but a moderately engaging one.