It's no revelation to note that Mark Ruffalo is a great actor, but it's been awhile since a movie afforded him the chance to show off his chops as thoroughly as he does in "Infinitely Polar Bear."

Ruffalo plays Cameron, the manic-depressive father of two girls who is tasked with caring for them when wife/mom Maggie (Zoe Saldana) signs up for graduate school out of town, circa 1978.

Written and directed by Maya Forbes, and based on her own childhood, the movie resists all of the quirky cliches you'd expect from such a premise. This is hardly a nostalgia-tinged trip down the proverbial memory lane.

Instead, "Infinitely Polar Bear" is resolute in its focus on Cameron, a complicated figure struggling with the weighty responsibility of parenthood and the burdens of his own mind.

He's played by Ruffalo with total conviction, in a performance that exudes the anxiety of a loving parent unsure if he's capable of caring for his daughters. There's a real inner struggle conveyed in scenes filled with the desperation of a man forever trying to find his way to psychological freedom, a sadness and a sensitivity, but also a resolve to fight back against the demons.

There's beauty in the picture's cool, gray winter light, in the cramped but comforting apartment interiors, and in the way Ruffalo and the actresses playing his daughters (Imogene Wolodarsky and Ashley Aufderheide) seamlessly craft a relationship based around deep love and mutual concern.