Just finished watching the one on the Romans. The thing that struck me is the loss of basic knowledge by the majority of people in such a short period of time.
At one point most people pretty much knew how to do almost everything. For sure, there were specialists in various things - usually construction - but all in all your average punter could feed, house, and provide for themselves with nothing really but a few tools and a wealth of knowledge passed on through the ages. Now, within less than 100 years your average punter couldn't effectively hunt, build long term shelter, make fire, bread, or even store things without the assistance of technology.
Bizarre, and sad.