This is a great series, informative and educational. I can see why some reviewers on here think that it's "politically liberal" but that's because it's made by educated people at Smithsonian; who get their knowledge from academic science and historical research, not from ill-informed people on Twitter.
The big flaw is the level of background music on some (but not all) of the episodes. My guess is that the sound mixer monitored his/her mix at loud levels in the dubbing area, using high quality loudspeakers etc. That's great and probably impresses the client but if you don't pull back the music a lot more when the narrator speaks then this happens: On your massive monitors you can easily hear the narration under the music but at home, where the real customers are, they're probably listening on a tv with lower quality speakers, maybe even on something with compressed audio output. That's where all sounds are treated almost equally and the music and narration blur into one. Ever wondered why the narration is more audible on some episodes but not on others? It's nothing to do with your age.
The big flaw is the level of background music on some (but not all) of the episodes. My guess is that the sound mixer monitored his/her mix at loud levels in the dubbing area, using high quality loudspeakers etc. That's great and probably impresses the client but if you don't pull back the music a lot more when the narrator speaks then this happens: On your massive monitors you can easily hear the narration under the music but at home, where the real customers are, they're probably listening on a tv with lower quality speakers, maybe even on something with compressed audio output. That's where all sounds are treated almost equally and the music and narration blur into one. Ever wondered why the narration is more audible on some episodes but not on others? It's nothing to do with your age.