The problem that I've seen is that Germany diverts too many of its divisions elsewhere. For example, in my last game, Germany had about 40 or so divisions guarding from Brest to Copenhagen, another 10 or 15 in Yugoslavia (fighting Yugoslavia), and the remainder (about 70) against the USSR border when they finally declared war on the Soviets. It would have been much more prudent to have drawn more forces from the coast, and most certainly to have waited until Yugoslavia had been destroyed.