By day, they climb cliffs and learn survival skills. By night, they sit around a campfire singing songs and discussing philosophy. They're the Cash clan — and if their everyday activities haven't convinced you that the six siblings aren't part of an ordinary family, the determination and dedication of their father, Ben (Viggo Mortensen), should do the job. There's a reason that the heartfelt film that tells his tale is called Captain Fantastic, after all.

Whether he's running around the forest in America's Pacific Northwest, or making a scene by wearing a bright red suit to a funeral, the eccentric, affectionate Ben always seems larger than life, and much like a superhero to his kids. But, when tragedy strikes, he's forced to take them on the road out into the real world. With his oldest son Bo (George MacKay) also contemplating leaving his untraditional upbringing behind for a new college adventure, and his parents-in-law (Frank Langella and Ann Dowd) unhappy about his off-the-grid parenting methods, conflict soon begins to brew.

As the offbeat brood treks across the country in a coming-of-age journey for both adolescent and adult characters, Captain Fantastic traverses territory that feels familiar and fresh all at once. Yes, the path it takes is sometimes a little predictable, but writer-director Matt Ross generates enough genuine emotion to ensure that it also feels authentic .This is a warm, rich and vibrant production, both visually and in tone.

Continuing his spate of fantastic performances in under-seen fare like The Two Faces of January and Far From Men, Mortensen is more than partly responsible for the movie's charms. In fact, he's simply magnetic in a progressive, protective parent role that trades heavily on his gruff yet tender charisma. With much of Captain Fantastic dependent upon unpacking the many layers and contradictions of a man who gives his 6-year-old son a copy of The Joy of Sex but hasn't imparted his 16-year-old with enough practical wisdom to know how to talk to girls, the subtle complexity he brings to his protagonist couldn't be more pivotal. Around him, his young and experienced co-stars also shine, particularly MacKay and the veteran Langella.

It helps that Ross knows a thing or two about unusual families, with the actor-turned-filmmaker having starred in the polygamous TV drama Big Love for five seasons. While Captain Fantastic directs most of its fondness towards its unlikely hero and his eclectic clan, it also explores the importance of not only difference but balance. That's not an easy feat given how endearing the main characters and their unorthodox lifestyle are, and proves a testament to how multifaceted this smart, sweet picture really is.