Indeed I think that also Axis NA are good.
Germany has Atlantic wall that is good (infantry defends on 3 in the first cycle of amphibious assault) and Dive-Bombers, which I consider a strong NA: fighters hit on 5 in the first cycle of combat if there are not defensive fighter presents.
To have a fun and interesting game with NA, I think that they should be chosen by the player one at time at the start of their turn. In this way we found, in our games with NA, that the relative value of the NA is variable, depending also from what the other have chosen, and also that their interaction is a fundamental thing to consider in the initial planning.
I think, however, that USA have two very powerful NA: War Economy and Mechanized Infantry.
However, NA do not change so much in the game Strategy. Axis is always focused on conquering Moscow, as Jennifer said.