I played Japan last weekend. I didn’t have too hard a time, however I tend to play a very anti-US strategy. Therefore I was able to manage them as well as I had been able to in the Pacific game. I even had him spending more on the pacific side. Russia was actually what tended to throw me off because I had to constantly be prepared for a potential invasion until it was my time. Luckily I had set a trap and Russia invaded Korea, allowing me to trap him between my navy and land forces.
If your looking for more specifics then let me know, otherwise that should give you a slight idea as to what to expect.