It is a good movie. I am not going to say that every last detail was accurate. But from what I have read the details are far more accurate than most movies on these kinds of subjects.
My grandfather worked with Clyde Barrow in the oilfields in Oklahoma. Obviously, pre-bank robbing spree. Said he never would have suspected it was the same guy—just another roughneck trying to make a living in desperate times.
Probably the most relevant part to their story is how the press callously marketed their exploits against the public interest. Some things never change.