Maybe 40%. If that.
If you want to know the real story, buy the book "Ain't Too Proud to Beg" by Mark Ribowski. He interviews everyone he can who's still around (Otis, Dennis, surviving relatives of the others), and gives a somewhat more balanced view of the history than Otis' autobiography (which isn't fictionalized like the film - it just holds a natural pro Otis and Melvin stance).
A number of liberties were taken with factual events for dramatization purposes. For example, in the film, Melvin Franklin apparently dies outside of the kitchen in his mother's house. In reality, he died from heart failure at the Cedars-Sinai Medical Center after being admitted following a series of seizures. David Ruffin was not found dead near a hospital, and then taken to a morgue where he was properly identified. Instead, he had suffered a drug overdose, and was taken to the hospital by his chauffeur where he died there. Another inaccuracy is the depiction of Ruffin, Kendricks and Edwards performing together before the 1982 reunion tour, when in reality Ruffin and Kendricks did not start performing together until 1985, with Edwards joining them in 1989 after the group was inducted into the Rock and Roll Hall of Fame.
Otis Williams' ex-wife Josephine Miles, Melvin Franklin's mother Rose Franklin, Johnnie Mae Matthews, and on David Ruffin's behalf, the Ruffin family, filed suit against Williams, Shelly Berger, David V. Picker, Motown, De Passe Entertainment, Hallmark Entertainment, and NBC for use of their likenesses in the film, defamation of character, and emotional distress because of the inaccurate depictions of events. They also alleged that the miniseries misportrayed them and/or their relatives and twisted facts. The judges ruled in favor of the defendants, and the ruling was upheld when the plaintiffs appealed in 2001. Otis Williams later claimed that while his book was the source material for the film, he did not have a great deal of control over how the material was presented.