So, the great man has been praised, mourned and laid to rest in his homeland.

Now, in an apt piece of timing, comes the story of his life. Unfortunately, and as much as I'd prefer otherwise, it feels like a remarkable story told in an unremarkable way.

Based on Nelson Mandela's famed autobiography, it concerns the passage of his life up to becoming South Africa's first black president in 1994, all of which is entwined with his country's turbulent history of apartheid.

It starts with a glance at Mandela as a young boy in his tribal village in the Transkei, where he is given a forename that translates, presciently, as "troublemaker". But the film focuses on his adult life, from 1942 in Johannesburg, where he works as a lawyer who has the temerity to represent clients in courts dominated by white lawyers.

At first Mandela (Idris Elba) is a reluctant, even unlikely hero - a ladies' man unfaithful to his first wife and seemingly as devoted to his love life as to good works, a committed lawyer who doubts the ANC's potential for bringing change. But the government's increasing persecution of black South Africans - the enforcement of apartheid from 1948, the creation of black townships, the Sharpeville massacre in 1960 - all drive him towards greater engagement and militancy. "If they want a war," he eventually declares, "we will give them a war."

In this time he also meets his second wife, Winnie (Naomie Harris). They have two children before Mandela - whose sabotage of government buildings has made him one of the country's most wanted men - is finally captured, tried and imprisoned on Robben Island in 1964.

Thereafter what feels like a race through history understandably slows down, as the man who has become known as "Madiba" spends 27 years in captivity. As the film's subject becomes disconnected from the fight against apartheid outside his prison walls, the film loses some spark.

That said, as the white government starts to falter, Mandela's wily political instincts and innate goodness come into their own, combining in his negotiations for his release to steer the country towards a democracy no-one could have imagined.

The second half of the film also offers an account of much-maligned Winnie, who not only became the anti-apartheid campaign's visible figurehead in her husband's absence, fighting tirelessly for his release, but was herself imprisoned - including 16 months in solitary confinement - something that the film suggests hardened her personality. Harris is very good indeed at conveying Winnie's transformation from a joyous young woman to a tough, even cruel radical - a change in spirit that creates a wedge between husband and wife greater than his imprisonment.

Elba, too, is excellent. I don't think the actor could ever wholly hide his trademark rolling gait, and it's here sometimes in all its goofy glory. Otherwise, he disappears into his real-life character, sometimes unrecognisable not because of prosthetics as much as the commitment of the performance. And it's a performance very much as Mandela himself would have wanted it - warts and all.

If only the direction of the film was not so workmanlike. Justin Chadwick does elicit our anger, outrage and sadness when conveying the racism and savagery of apartheid South Africa - it's almost impossible not to. At the same time, his pacing of the narrative often sags, and the tone feels unnecessarily staid. To be fair, there is an awful weight of history upon this; but I'm not sure the film needed to replicate that history's very long walk.