I believe Germany is very much the hardest to play as, because it is very very easy to mess up and you’re surrounded by two countries.
You will find that if you try to rush Russia that you will get heavily delayed by his infantry tactics since your IC is far away, and then UK will come out of no where into the baltic, which borders 4 of your territories, with many transports and fighters. Your attack on Russia will stall and die, while he slowly pushes in, while you’re dealing with the UK invasion.
With Germany you have to make very very hard decisions on what to do. This is not nearly as true with UK for instance. UK is very easily defended and he has a great safety/mobility in where he attacks once he blows up German navy. Also not true with Russia, just as Russia just keep stalling on the west front and if Japan starts coming in you have an incredible amount of time to build up infantry to defend against it.
Japan is also difficult to play as. It’s not difficult at all to fend off the US fleet, but it is difficult to make big land grabs because how long it takes to really get into Russia and how you’ll never have a big enough attack force with infantry moving so slowly by the time you get there. Also a British IC in India can really put a thorn in your back if he starts island hopping while you’re fending off a US naval swarm.
I could be very wrong, but the Allies have generally really good defending positions and have very little to think about, just respond to what the Axis is trying to do.
I would like to hear good German strategies, but so far the one I’ve always been trying has failed massively (try to take out Russia first). Good Russian players can really defend well until the UK invades Norway and such. And if you can’t keep up pressure on Russia, your outlying territories will wither under growing numbers of Russian troops until Russia overcomes Germany IPC income.