I dont think there are any big balance issues in the game. The better players usually win and if the teams are even we almost play for 15 hours and are not able to call it (unless grave mistakes are made). The problem i have with the game atm is more that it is not as dynamic as it could be.
I think there are a few changes that could make the game more dynamic.
The first would be some sort of Vishy rule. Say there is a minor axis ally formed in southern france and some of the colonies when france falls while the rest are free french and work with the Britts. There might be a need to redeploy/add/remove some units to compensate for this, mainly in the med.
I also think there should be an european NO for the americans (tourch is a good one), the alaskan or mexican one could be removed if needed to compensate for this.
Furthermore i do not like how grave it is to loose ones capital. I think there should be some sort of exiled capital rule. Say if a capital is taken the attacker gets all the defenders ipc on hand and that the defenders income collection rate of the power with an occupied capital is halved. I think this could be a potential way of fixing all the silly all-ins that are used in the game.
I also have some problems with ANSAC being a power in itself. I understand the function in the game as the set-up is now but i would rather have it as a third part of the CW with is own economy (Canada could possibly also be a separate economy and there could be some sort of transfer system, its might make things more complex but it could also be alot of fun).
Last but not least i would like some sort of micro IC:s say for the cost of 5-6 IPC that could be built anywhere (or in areas with an IPC-value of at least one) and that could build one unit (maybe not capital ships or strategic bombers). This could make remote parts of the maps more interesting. Russia could build one in the far east, Italy in East Africa and the Japanese or the Americans could build them on islands in the Pacific. Combined with the free french and the exiled capital a rule like this could generate alot of interesting options.
All of these thoughts are untested. They are just things i i think would be interesting to try out.