It is difficult to believe any film could do Muhammad Ali justice.

That Michael Mann's biopic has apparently failed to capture the drama of an extraordinary life is, paradoxically, testimony to Ali's greatness.

And perhaps it is kinder to put the film's supposed failures down to Ali's colossal standing as a person rather than Mann's shortcomings as a director.

Mann chose to cover a 10-year period from 1964, when the then Cassius Clay beat Sonny Liston for the heavyweight crown, to his astonishing upset of George Foreman in 1974.

It was undoubtedly Ali's defining decade, but in focusing so closely on one period, Mann ignores great, pivotal swathes of Ali's life.

What of the middle-class black kid growing up in Louisville, Kentucky and the forces that moulded a shimmering personality?

Or the crushing pathos of Ali's last fights and subsequent struggle with Parkinson's disease?

In Mann's defence, Ali's three year ban for refusing the draft must have been a contemplative time in his life, but it leaves the movie open to criticism for failing to cover crucial periods.

On the boxing front, the film deals principally with "The Greatest's" unlikely victory over a fearsome Liston (Michael Bentt), his trilogy of fights with Joe Frazier (James Toney) and the "Rumble in the Jungle" with Foreman (Charles Shufford).

The ring scenes have been well received and it is rumoured that Smith had to accept numerous blows from his on-screen opponents.

But despite the authenticity of the scenes, critics have bemoaned the fact that the scale of Ali's triumphs are not accurately represented.

Lest we forget, Ali's defeats of Liston and Foreman were two of the biggest upsets in boxing history.

Away from the ring, Ali's religious conversion to Islam is a central theme, but his beliefs and feelings have apparently not been examined in great depth.

For example, while his connections to Elijah Muhammad's radical Nation of Islam are stressed, the fact that Ali never accepted its belief in separatism or in whites as "devils" is ignored.

And while Ali's wives and lovers are introduced, his notorious womanising is not a huge feature of the film.

Taylor Hackford and Leon Gast's joyous documentary, When We Were Kings, succeeded because it had Ali himself in the title role.

Smith reckons he peaked as an actor with his portrayal of the great man. The problem is, when you have had the real thing, anything else is bound to disappoint.