Every new WWII documentary faces the same problem: there is hardly anything new to report. The history has been written - there is no sudden new evidence. What differs are the interpretations. If you know this part of history there isn't much to look for here but a reminder of how cruel the war was.
As for the material itself: what is described as "rarely seen" is actually quite common and has been seen in many series before. There was not much new for me. In at least two parts they were even using movie footage from cinema. The "expertly restoration" is as good as can be expected. The source material just isn't that good. There is no HD to get out of this and the colors oftentimes look wrong. It's almost unrealistic at times. I was never a huge friend of those altered footage to beginn with. I am also not in favor of the term "greatest" as it implifies a certain glorification. Maybe "Biggest Events" or "Most Important" would have been more appropriate.
Should you skip this, then ? Not necessarily. It is a good starting point for someone who's interested in WWII history. Those who already know it can use it to fresh up the memory. Just know what to expect.