This film exhibits all the problems of telling real events in a dramatic form.
Will Smith does a fine job of imitating Ali but the script has no structure. It simply strings together events over a fifteen-year period.
Ali goes through change but not character change. For example, he refuses to go into the army, but since we only see him as a celebrated champion, his insistence that the Viet Cong have not infringed on his rights in America rings hollow.
A bigger problem in this film is the lack of plot. Plot comes from hidden information revealed. Everything in this story is on the surface. And since the events of this story are fairly familiar, the narrative drive disappears long before the movie is over.