Having played G40 A LOT, I have a different take than Gamerman on the problem with it.
I think the main drawback is that with larger map and air/naval bases the moves are automatically limited and easily anticipated, reducing any fog of war element and requiring a vigilant player to spend a lot of brain power figuring out what his enemy can do and counter it.
In this respect G40 is more like chess than traditional A&A.
The solution? Ironically I think the solution would be placing a lot more units on the board and more tech that’s more easily accessible. This would mix up the possible moves enough so there would be no point in trying to run all the permutations. This would also probably extend playing time, but that wouldn’t bother me.
The only other way to solve this issue would be to introduce a bunch of crazy “limit rules” on movement, such as: You can’t invade southern Italy until you control Sicily, or you can’t invade Japan until you control both Iwo Jima and Okinawa… Or you can never invade Germany by sea…etc.