I found the idea of the film intriguing. If allied Japan and Germany had won world war ll, we may have seen 1950 cars in the 60s and other manufacturing progress at a much slower pace than actually happened as portrayed in the series. However, science progressed as did the Arms race. So did music in the neutral zone.
The idea of parallel worlds is an old one. I find that overall it’s a bit choppy and difficult to follow. More so on series 3 and 4 than in 1 and 2, as if new writers were skipping links from one show to the next. However, overall it is thought provoking and entertaining.