Directed by Michael Mann starring Will Smith, Jon Voight and Jamie Foxx.

When Michael Mann announced that the subject of his next film, the self-proclaimed 'Elvis of boxing', was to be played by Will Smith, it seems fair to say that many, yours included, expected the worst. While Smith proved his acting credentials way back with 'Six Degrees of Separation', subsequent fare like 'Bad Boys', 'Enemy of the State' and 'Wild Wild West' weren't exactly praised for their dramatic content and the overriding fear was that Smith's Ali would be a case of the Fresh Prince aping 'When We Were Kings'. Well, the actor with the big grin has had the last laugh, because Smith has silenced his critics with a performance, which has deservedly made the Oscars shortlist and is also the biggest plus point in a worthy if somewhat unsatisfying film.

From his cinema debut 'Violent Streets' through to 'Manhunter', 'Heat' and 'The Insider', Mann's films have moved at a slow, character-developing pace, giving the audience a chance to try and understand, like or dislike the complex people who inhabit them. 'Ali' too works off a similar time frame, but it offers few insights into the man or his entourage that you didn't know already.

The difficulties in bringing anyone's life to screen are great and conducive to shortcuts, so Mann has wisely chosen the decade from 1964 to '74 to chart the various sides to Ali: contender, champion, black Muslim, outcast and back to champion again. In every scene the director's sense of the era is superb: the constantly on the boil racial tension is deftly depicted and the filming of Ali's time between the ropes resists temptation and concentrates more on the sights not sounds of battle: the expectation, fear, bravery, resignation and triumph in the combatant's eyes.

But while all of the above elevate 'Ali' far above routine biopic fare, they offer only the public, not the private, aspects of the man. Ali's family background needed more time (his first wife literally disappears after an onscreen argument about what she's wearing), his links with the Nation of Islam, which existed alongside his friendship with whites, are never properly addressed, while his dynamic with trainer Angelo Dundee warranted more time than the odd worried look and daub of gauze between rounds.

But that's where Smith comes in. Granted, as the star he has to carry the picture, but the fact that he carries it when nearly all the supporting cast are little more than outlines (the exception a great Jon Voight as Ali's TV sparring partner Howard Cossell) means that he's deserving of the highest praise. Bulked up and broody, Smith clinically nails Ali's voice and moves but never gives the impression of having learned the man off by rote.

Of course, you know how it's all going to end – in this case Zaire and Ali's career defining victory against George Foreman - but to Mann's credit you will still want to climb up and wade through every peak and trough in Ali's life. And he knows how to stage a set piece: the epic finale is breathtaking in its execution and compensates for the heavy scenes where the film drags at an almost reverential pace.

Given how this film could have turned out, Mann has emerged with only a few cuts and bruises, while Smith to paraphrase his character, hasn't a mark. Ultimately 'Ali' is a film where style gets the better of substance, but for Smith and the finale you really should take your seat ringside.

Harry Guerin