2,5 hours is of course way too long for a film, but at the same time very short to depict 70 years of an intrepid and eventful life.
As a consequence, this opus is decidedly better as a history lesson than as a work of art.
As a history lesson, it worked fine! Roughly a hundred senior-high school students sat stock-still throughout the film, and learned a lot while doing so.
Even I, who knew the story, resent biopics and execrate long films, didn't really have time to lose interest. Contrary to Mandela's autobiography, this film does not gloss over his womanizing or Winnie's propensity for violence.