I've probably read and watched a combined more than one hundred books and documentaries about the Third Reich, and there is little to nothing new, that was previously unknown, revealed by the "lost tapes."
What is new is the blatant propaganda contained in some of the cut-to-commentary scenes in some of the episodes. Really, it would make Goebbels himself blush. There are good episodes and segments, but some of the commentary is absolute rubbish.
In everything I've ever read or seen about the Reich, this is the first time I've ever seen it suggested that Hitler used the phrases "Make Germany Great Again" or "the press is the enemy of the people." I believe this to be a highly slanted and subjective translation of the German in order to try to draw parallels to a certain modern politician.
Among the most laughable injection of modern bias was when they suggested that Hitler would talk about "fake news," with the implication being obvious. What makes it laughable is that the people that wrote this script either don't know, or have forgotten, that it was CNN that coined the phrase and was the first to try to use it to smear information they didn't like -- in one of the most spectacular backfires of modern political history.
If they wanted to draw more serious modern parallels between Hitler's desire for total control over the freedom of information and speech in the Reich, they'd do well to examine the anti-free-speech actions of the likes of Facebook, Jack Dorsey's Twitter, and the intelligence operatives that told you a certain laptop was fake - when it wasn't - and changed the course of history.
They got almost entirely through the discussion of the Nazi invasion of Poland before throwing in, as a last second footnote, that the Soviet Red Army simultaneously invaded Poland from the east.
All in all, a mediocre rehash of the rise and fall of Hitler, and take the modern commentary through a filter for sure.
If you want a MUCH better, deeper, probing of the personality cult that was Hitler, hop over to Netflix and watch "Hitler's Circle of Evil" which is a spectacular dive into all the personalities of this dark chapter in history.