I have to dispute the prior review. This is historically accurate up until around 1924 or so and then it diverts. The prior review reports that it isn't realistic. This is alternate history. It relies on those involved thinking differently, taking different choices, etc.
I have a degree in history and this novel actually made few changes. It takes into consideration very real alternate military campaigns (Raeder's North Africa campaign vs. Sea Lion) and removes other obstacles (the author clearly not having FDR as president in the 1940s if Dewey is president during the German attack).
There are too many people out there who either write really bad Nazi wank or who believe the Germans were way too extremist and radical to win. This novel does a good job of balancing the two views and presenting a possible what if. You may not like a victorious Hitler, but his failure was not always a certainty. Give it a peek. It's free afterall. I gave it a chance and loved it.