Overall I really like ths game. It is fun, relatively simple to learn and has enough variability to keep replay value high. Certainly some things could be tweaked but I don't see anything really major tht needs to be changed.
There are a couple of things I wouldn't mind seeing done if possible.
1. Would it be possible to make any hex upgradable for AA? Also hex AA should be able to damage any type of air unit that attacks it.
2. The unit upgrades available could be tailored better to make the units more useful in the roles they were designed for. For example perhaps Carriers should upgrade to ASW, Advanced Air and Naval Attack if only 3 slots are possible and BB's upgrade to Artillery, Surface Attack and AA etc.
3. Sometimes it seems like Tech upgrades are too random. I've gone into 42 as Russia without getting Infantry Weapon 1 even though I usually start researching it in 39. Perhaps something could be done to make low level tech easier to hit on once all of your allies have it.