I'm at the end of 1941 in my first game as Axis. I am playing a "delayed aggression" strategy in both Europe and the Pacific, with the Axis focusing on the Mideast and Africa in preparation for a spring 42 attack on Russia, including opening up another front via Persia from Iraq. Similarly I'm planning on a spring 42 opening of the Pacific campaign with a standard set of attacks on Pearl, Singapore, Phillipines, etc.
However, plans for both theaters went awry. To start with the Pacific and the US, in November 41 the US mobilization is at 82%. Though Japan did nothing provocative in that turn, US mobilization shot up to the high nineties in December (tried a few reloads, seems to always happen) and Prepared for War. To the devs: is there something hard-coded that brings the US into the war in 42, whether Pearl Harbor happens the previos turn or not? Seems buggy to me.
As for Europe and Russia, the Russian mobilization did kick up when Egypt and Iraq fell. This seems reasonable. However, it advanced a lot faster than expected. I wasn't watching it carefully, and Russia wound up fully mobilized in October 41, and declared war. The Axis was in mid-preparation for a spring war, so this leaves the whole front in a mess.
I'm not sure if these reflect bugs, or things are working as expected. If the latter, I find it highly ahistorical that either the Sovs or the Americans would declare war in these circumstances. While there was no love lost between Soviet Union and Germany, I don't see Stalin opening hostilities except in extreme circumstances. One can argue that there needs to be some mechanism for forcing Germany's hand. But by when? Personally I'd love it if the game supported an option in which Russia and Germany never come to blows, but Germany uses other strategic options like Seelowe. Perhaps Russia and Japan could fight, with Germany neutral?
Likewise, given isolationist politics in the US, entery into the war without a clear provocation (like fall of London, invasion of Canada), and missing the high moral ground that Pearl Harbor granted, seems unlikely in the extreme. Another thing: when Russia declared war on Germany/Italy, the US shrugged. Seems like this would push their mobilization back due to isolationism.
One possibility that wouldn't change Strategic Command too much: allow US and USSR to sit at 100% mobilization without entering the war. Once at 100%, it takes some event to allow them to declare war.