Opening Friday at AMC Quail Springs Mall 24, it’s a Canadian film based on Mordecai Richler’s 1997 novel, detailing the entire adulthood of Barney Panofsky (Giamatti, TV’s “John Adams”), who, despite being wildly successful as a soap-opera producer, fails spectacularly in his personal life. It takes him three marriages to get it right, and even then, he manages to screw it up.

“You wear your heart on your sleeve, Barney,” says his first wife (Rachelle Lefevre, “The Twilight Saga: New Moon”). “Put it away. It’s disgusting.”

For most of the time, the film is so amiable that audiences are apt to overlook its faults, primarily of trying to tell so much story that it ends up saying so little. Giamatti is likable, even when Barney is not; his failures are played comically, especially when Dustin Hoffman shows up as his filterless father, and the middle stretch that details Barney’s second marriage to a spoiled Jewish princess (Minnie Driver, “Conviction”). Their union is doomed from the start, considering that at their reception, Barney meets the woman of his dreams (a splendid Rosamund Pike, “Made in Dagenham”) and asks her to run away with him.

An otherwise enjoyable movie does an about-face for its final 30 minutes (of an overlong 134), suddenly cranking its notch to “melodrama” and milking the theatrics as it were a Lifetime disease-of-the-week premiere. At that point, director Richard J. Lewis ditches the humor and subtlety, losing a firm grip he never regains.