My two cents:
IC system is rather solid, however, needs some tweaking to make things more balanced.
World trade and the resource system needs a better look-see... Resources should be a major problem, and when the Axis go to war and their main sources of trade are cut off (or nearly so... should be a much greater hit than 50%, IMO), the situation should become rather desperate. The Germans and Japanese got virtually no oil from trade after a certain point... it just didn't happen. That's why Ploeisti and the conversion plants were so important to the Germans.