While at work I heard two people discussing the movie and ripping on it because of how historically inaccurate it was. They were talking about bad leaders and quick to surrender French and other typical armchair General stuff. If they had read this book, they probably would change their tune.

The entire situation was a giant clusterfck. Communications were sporadic if even available. Panic was at a high. The bravery of the BEF and French soldiers that held back the German advance can not be overlooked.
The book uses many first hand accounts of what was going on during the two weeks or so leading up to and during the evacuation which brings a nice personal touch instead of just listing large numbers. Also gives a sense of frustration that many of the soldiers must have felt when you read about someone who has lived through a week of pure hell only to have their ship bombed a mile off the coast.

I haven't seen the movie so I can't compare the two of them.