Hm, moves and opportunities.
Well, for one thing both the UK and the US opened with quite risky moves and then had quite bad luck with those moves. This backfooted the Western allies pretty badly from the get-go.
Also, I think the Americans should perhaps have built an industrial complex in Sinkiang to help slow the Japanese advance. That could have made the difference in the long, drawn-out battle over India/Indochina that the British were engaged in. Also, as I noted it was actually possible to build this IC and get a build in rather late in the game by blocking the Japanese advance.
Also, losing naval supremacy in Europe to Germany was a disaster, since it allowed the Germans to pretty much ignore the British.
I think that is pretty much what I remember of specific moves. I'll add that I liked the aggressive British play in the Pacific islands and that Japan and Germany generally played very well.