I agree that the second programme was not so good. The coverage was very uneven, neither first nor second world war defensive buildings were fully covered.
The "Chain Home" interwar radar towers were ignored, but the sound detection mirrors, that led no where, were emphasised.
Why not a programme to each war, two invasions for the price of one?.
The actual invasion of the Channel Islands, and the huge overground / underground building by the Germans there seemed to pass by. Is it British Isles = England.
After all the construction implications of WWII in relation to airfields alone could have warranted a show to itself. The sheer scale of the building by the UK, and by the US forces, even in terms of impact of concrete on the landscape or of employment could have been treated.
Still better than nothing.