I suppose a hallmark of a good "based on a true story" story is when it takes a twist that seems to come out left field and the screenwriter can just point at reality and say "it happened". American Gangster takes just such a twist late in the 3rd act. Which is good because the first 4 hours* of the movie are very well made, but almost a little too perfect screen-written to be true. Of course Denzel Washington's titular gangster is a family man and polite to a fault. Of course Russell Crowe's cop is too honest for his own good and has a terrible personal life.
FuzzyCo grade: A
* An exaggeration. I think the whole movie is only 8 hours long.