I’ll just add my ignorant two cents’ worth…
This question goes to what I think is the heart of the game - logistics. The Allies start the game with an economic advantage (greater production) while the axis have the logistical advantage: they build their troops right close to the action. This means that the Allies economic advantage is a bit of an illusion - they cannot actually build more, at least in terms of fighting units. To get 8 IPCs of fight to Russia’s doorstep, Germany only spends 8 IPCs. The US and UK have to spend 16 IPCs to deliver the same fight - the armor, the infantry, and a transport to carry them.
(Actually, that’s why I think Russia is a bit under-rated. Sure, the production sucks, but what production there is is right on the front, and can be immediately used where it is needed.)
So the heart of the game then as I see it is whether the Allies can efficiently overcome their logistical disadvantage in order to realize the benefit of their economic advantage. A Norway IC is one solution to that, but thinking about it, I don’t think I like it. It delivers units to the front more quickly than any other solution once it is built. But it takes time to capture Norway and also time to build the IC. It also lets Germany know where the attack will be coming from, and as Sun Tzu says, deception is the key to all warfare. That said, if Norway could produce more than 3 units, I might think about it more.
I’ve only played about five games, but I think this is why I won and why I have seen people lose as the Allies: quite simply, they fail to get their IPCs delivered to Germany’s doorstep. They build units that they won’t have the transports to move. Or they build enough transports, but fail to protect them from attack. Or they build extra transports that won’t have anything to carry the next round. Any of these result in wasted IPCs sitting around on Great Britain (or in the water) while German tanks roll happily across Africa and Russia.
So I think the key to the game is simply planning carefully how to get (or prevent) Allied IPCs flowing into Europe (or Japan) as efficiently as possible, and thereby realizing as much as possible the economic advantage. This means getting control of the sea while preparing an invasion fleet that wastes no IPCs. The Axis meanwhile have to leverage their logistical advantage to prevent the Allies from setting up an efficient delivery system.
Another thought I’ve had for getting Allied IPCs across is in the form of fighters. They can arrive to help defend Russia in one turn, and avoiding the sea means that Germany’s navy is all a complete waste. The problem though is that they can’t support Russian offensives, and are too expensive to use to attack on their own. But they might be a good interim idea while the shipping gets set up?