Not the greatest movie about The Greatest, but pretty damn good.

Rating: 7/10 (30 December 2001)

Just a few comments to balance out what others have said:
Will Smith already proved in "Six Degrees of Separation" that he CAN act. He was very good here. Not Oscar-worthy in my opinion, but a very good job nonetheless. More impressive for me were Jamie Foxx (who also impressed me a lot in "Any Given Sunday") and Nona Gaye (who I didn't know had any acting talent at all - but I guess she does).
This movie, like a lot of Michael Mann films, sets a tone, an atmosphere, and goes with it. That's the reason for overlong scenes like the opening nightclub scene and the jog in Zaire. Tell me that after the opening scene, you didn't get a great feel for the 60's - the period in which most of this movie takes place.
I will defend the jog in Zaire scene too - Roger Ebert even complained that it went on too long. But during the scene, I was thinking lots of things - "I wonder what Ali is thinking?" "I guess he's thinking of how different his life is than these poor people. He's thinking how much of a hero he has become to people he doesn't even know. How much responsibility he has to win the fight because these people all support him. How Africa is his peoples' homeland and how he's basically come home." All those thoughts went through my head and I think that's exactly what Michael Mann intended. The scene NEEDED to run on and on to convey all those different thoughts and ideas.
At the end, I admit I was a little disappointed because I had hoped the film would cover more of Ali's recent life including battling Parkinson's disease. But I guess that's for Ali 2.