I find Global '39, despite the basic mechanics, to be quite a bit differnent than Global 40. I got fed up with G40 after we got into Alpha 3.whatever. Global 39’s rule issues are mostly those of clarification. We’re not dealing with constant swings to deal with major (perceived) balance issues.
It’s just an opinion, but Global 40 became a mess I did not want to play anymore. I have (not to mention the group I play with) had more fun with Global '39.
Global '39, to me anyway, takes the best from all previous A and A incarnations (including after market stuff like Zeno W@W), adds some original stuff for AandA (like the Axis minors and a d12 mechanic) all on a really, really big, beautiful, so-good-you-wanna-fall-down-and-thank-the-AandA-gods-for-it map.
What’s better yet is that HBG continues to make Global '39 better with optional rules and markers (not that they can’t be used for other AandA variants, but I get the feeling they are more directed to HBG developed games).