First, in defense of the series against some of the review comments about the source of the video, just because you've seen it in a movie doesn't mean it's not real wartime footage. Older movies, before CGI, did that all the time to save money. For instance, we've all seen that crash of the plane onto the carrier deck in a movie or two, the one where it breaks in half and spins around. But it's real, not shot for a movie.
Second, there's no way to cover everything important that occurred in WWII in 10 hours so obviously many important things will be left out. You can't cover the contributions of every country when so many participated so you pick the major combatants, etc.
My main complaint is in many cases they cover some subjects in such a way as to focus on a more minor topic and leave out the major one. So many examples I can't list them all but here's just one: in the Battle of Britain episode they extensively cover the Spitfire without even a mention of the Hawker Hurricane when in fact there were many more Hurricanes used and Hurricanes were responsible for many more German losses than Spitfires. Yes, the Spitfire was the shiney new plane at the the time. But it's higher complexity meant lower percent availability of the smaller numbers of planes and the Hurricane's quicker turnaround time meant a single Hurricane could fly more sorties in a day. So why not take even 20 seconds to mention the most important British fighter in the Battle, especially the early stages?
