My few suggestions=
-Tweak the AI so that minors / midgets don't build dozens of Interceptors, just 4-8 squadrons.
-Reduce the amount of resouces a bit, there seem to always be plenty of them.
-Check what happens after Italy surrender event: they stop researching after a while. Problematic when they surrender to the soviets.
-No ministers and leaders for England, Wales. Too few for Vietnam.
-Add option (event?) to never build any nukes.
-Make Japan AI more aggressive - they always stall in their pacific campaign.
-Create some civil war events for Greece, Italy after ww2.
-Free French forces are too strong and they also get a LOT of resources.
-Increase initial research speed by 5-10 percent, I never am up to date in 1945 even with majors, even researching at 180+ %.
-Tweak the division strenght option for some strong minors - I've seen Hungary and Romania having 30/100 strenght divisions,
it gets annoying with countries with few leaders like Thailand.
-Add some tech teams if possible.