I think what I like most about this movie is that it knows how the boilerplate biopic formula should be presented.
When you stretch a narrative over the course of ten years, it tends not to work especially well as drama. And that's arguably the case here: we don't get much insight into Ali's state of mind, most of the subplots (especially the ones involving Drew Brown and Malcolm X) are extremely underdeveloped, and it all starts to feel very connect-the-dots after a while.
But what Michael Mann gets is that this episodic structure lends itself much better to montage than it ever could to realism. So he instead turns the whole thing into a hazy, impressionistic spectacle, using music and vivid imagery and a feverish blend of film and digital cinematography (those nighttime workout scenes really anticipate Collateral and Miami Vice) to create a brooding, soulful, myth-making whirlwind. We may not learn a whole lot about this man, but it's incredibly easy to see why he was bigger and more legendary than any of us could ever hope to be.
Bit of a shame that this style peaks so early in the movie, though. Those first fifteen minutes are so striking and stimulating that the remainder really has nowhere to go but down.
Grade: A-