It's too kind to call this a "fictionalized" account of the Barker gang. They got the names right, but that's about it.
Russell is still hot, I'll grant you that, but this is not the real Ma Barker, who basically took care of the boys by cooking and assisting when they moved around the country, not by planning or participating in the crimes. I think it would have been far more interesting to present the real story of a middle-aged woman caught up in the criminal activities of her children and their cronies.
I also have to agree with those reviewers who found the shoot-out scenes to be totally unbelievable. The Barker/Karpis victims were a combination of the innocent and of the law-enforcement agents who pursued them, but they definitely did not mow down half-a-dozen FBI agents every time they were cornered. (On the other hand, as several recent books have related, the FBI of that era emphasized the idea of agents coming only from legal or accounting backgrounds to the extent that many agents had very little law enforcement or firearms experience. They were not the well-trained agents that we picture today.)
But the worst sin of all is that the movie is basically a bore. Nobody changes, nobody grows. We know the end of the road is ahead, we just don't know which shoot-out it will be.
Only for die-hard Russell fans.
