Between equal players, I believe the game is very balanced. I have received a few emails about one side getting smoked by the other early and what this means for the game.
I think it is important to be guided a bit by history, but don't be completely mislead by it. For example, just because France fell in 6 weeks during the war, does not mean it necessarily will in this game - especially if Germany does not prepare for France at all. I have seem Germany get defeated in 1940 because the German player assumes France will be a push over and builds lots of subs and factories and no army out of the gates. The German's in the real war prepared for France - and a good German player in this game will dedicate most of their builds to army units for the first few turns of the game as well.
On the other hand, the Allies can be just as guilty about being mislead by history rather than being historically driven. If the British completely write off France as a lost cause and don't put a BEF on the continent, France may fall much faster to a determined German player. The extra "free-time" then available between the Fall of France and Barbarossa puts a lot of pressure on Britain all alone trying to stop Axis aggression everywhere.
So, from a balance perspective, it is good to be guided by history to be able to win this game. But, not to be mislead by it.