Im have played 4 games as the allies, against two different opponents. I have won three times (although one of those games was won with ridiculous lucky dice rolls) and the fourth time was a draw. Due to time we had to stop and everything was still open, no clear winner.
I think the allies must be very patient. The US fleet must play a game of threats and small gains. I mean always be in a position from where you can threaten several targets. So Japan must increase defenses all potential US targets. And as the US you should always get all the small island that you can. This severely limits Japanese flexibility.