I think it was a tremendous help towards the German cause that their factories produced at 125%. That was one of the last things I did before the Axis was taken over by lion of judah. The upgrade basically allowed Germany to build 4 factories, and get 5 factories production out of them, while saving 200 PP, by not having to build that 5th plant.
I also found that the Allies, early on should have blocked the naval passageways to the North Sea, and through the Channel, with their subs, to prevent german Uboats from escaping into the Atlantic. It´s about 5 hexes that need to be covered, with submarines. Having to fight those submarines each turn to get out, was one of the worst things I have ever tried.
I also think that the allies gave up to early on the Night Bombing campaign. Early on the only defence Germany had was about 20 Night Fighter Is and 2 heavy flak in each obvious target. I also think that it was dead stupid to try and bomb somewhere that had a navy parked in it. As the navy gets to shoot back.
I found that in the beginning speed was of the essence, that Germany had to keep a good pace, and do surprising things, so as to constantly keep the allies guessing, and had the Soviets tried early to attack the Germans, especially while they were occupied sweeping through Europe that would have been the end.
I think Frank essentially wasted the German fleet, in an attempt to send it towards Britain. It should have stayed in the Baltic, and shelled everything along the coastline there... Also I was very frustrated that Stockholm was not overrun...
Lastly, and not applying to later versions of the game, since counter battery has been removed from the game. The French essentially wasted their artillery, in the maginot, bombarding the German artillery across the river, thus losing alot of it.