I've only been able to see two episodes of this series but it appears to have been well written and executed. There are no talking heads, just newsreel and combat footage.
The format is this. A question is raised: Why did Hitler stop his panzers before Dunkirk? Whence Stalin's reserve armies? Then an attempt is made to answer the questions. The writers give reasons that sound plausible to me but, properly, they don't come to any firm or simple conclusions. You'd have to get into Hitler's or Stalin's minds to know for sure, and even if you were able to, there are some really crepuscular recesses in there.
I won't bother to spell out the series' attempts at answers to these two questions. If you want to see a fuller exploration of events leading up to Dunkirk and Stalingrad, I recommend the Battlefield series from 1995.