I played a USA campaign on Strong Axis - Aggressive to test things out and I enjoyed it quite a bit, especially while observing the world waiting for my turn. The AIs, each on their own right, were quite competent against each other, and played mostly historical. Things got a little messy when I became involved though. Here're some of my observations:
- Japan started by doing somewhat poorly against China, but they regained momentum after a bit, both I was happy to see since I'm used to AI Japan rolling over AI China. But after Pearl Harbor, Japan simply entered naval battles piecemeal against me in the Marianas and by new years 1942 they no longer had any capital ships. I guess teaching a HoI AI about naval matters is a gargantuan task so I'm not complaining, I'm quite used to it
- UK and Italy had a stalemate at El Alamein until I joined (after Vichy France joined). They successfully invaded Syria in 1940 but when Iraq joined the Axis they crumbled and Iraq reached all the way to Suez until Iran entered the war and annexed Iraq. Iraq achieved that with less than 10 divisions while the Commonwealth had about 40 stuck around Egypt. This should've clued me in to what will happen later: AI failing to redeploy troops against emergent situations.
- Both in my invasions of Italy and and Korea/Manchuria I failed to see the AI redeploy anything to counter me. I already didn't think Italy could provide resistance, but I was disappointed to see that after Italy collapsed, it took me a week to annex the Social Republic, and slightly more than a month to reach Berlin with cavalry, only encountering piecemeal infantry divisions marching around. They deployed about 50 divs to France to counter my move from Italy to there, only to be reduced to a pocket when I took Berlin-Hamburg axis since they couldn't form a front in the middle. Before I had moved on Germany, they were on the verge of encircling Moscow, having taken everything between Archangelsk and Rostov.
Germans had about 300 divisions total and I was invading with 70. I didn't have any real superiority over them in quality either - they beat me plenty of times in central France when my Armor met theirs - but they couldn't form a cohesive front all around, only in places, and they were very sluggish in moving troops from the East. The Soviets could only start breaking through by the time I was in Poland so I assume they simply chose to maintain the front there, which seems problematic.
I hope this can be useful for your purposes! I'm planning on playing as Germany or the Soviets another time where I'll have less opportunity to cheese the AI hopefully.