We're now on ep 6 of the second season, and have to agree that this is one of the best programmes of the past few years, the equal of many of the more widely-acclaimed fave's IMO.
I'm more of a sci-fi rather than history buff, but clearly PKD thought through the alternative history very carefully, and you don't have to know much about WW2 to see that it could quite easily have gone the other way, particularly if (as in TMITHC) the Germans had further capitalised on technological advantages.
As you said, they have paid a lot of attention to the production design, especially Berlin, so it's a very convincing world.
I also like the usual PKD themes of uncertain realities/parallel worlds.
(I wonder whether there is also an intended/unintended pop at US hegemony/imperialism?)