Based on the previews I thought to myself, "another fake idea that the Nazi's could have won the second world war." Many war game simulations have shown that if the allies had not been able to win, then the next most likely scenario was that the communist would have won. MIT found that out on their computers, as did many other studies. To some extent the communists did win, since they took over most of eastern Europe. The Nazis (or Axis) powers only won in less than 10% of the scenarios.
However once I actually viewed this episode I was really pleased to see that the writers were not making this mistake at all. The WWII nations were only being used as pawns in a temporal political game of powers far greater than the nations of the mid twentieth century. This is a much more powerful episode, and is not based on a poor understanding of military history at all. The reason the Germans overcome the Americans is because of manipulation by masters of the Temporal Cold War - which I guess by now is a Temporal "Hot" War. This is a fight between "Time Lords" to borrow a phrase from another time travel series - Doctor Who. The writers are much better than it originally seemed to be at first glance.
In all, my "after" evaluation was much higher than my, obviously flawed, "before" evaluation. It shows that you should never judge a book by its cover, nor an episode by its previews.