It sounds like we need a new WW2 game written by the developers of Gal Civ 2 - that resembles a lot of Gal Civ 2s dynamics.
Countries/areas instead of planets though.
Nations instead of players. Invade another country - or move you troops in to an alied/friendly nation.
Economy and research would work just like Gal Civ 2. Research Radar - or anti-submarine devices? Or gas devices, better troop weapons - bombers, or better fighters (hurrican vs spitfire)? Spend time developing special troops?
How much to spend on recruiting spies? Bribes to foreign governments?
You'd develop tanks to help support troops. Build facilities in each of the countries you own (e.g. facilities to build things, research centers, special things like better troop training).
Build ships to transport troops etc across the water.
Use assassins?
Do a propaganda campaign (influence the "influence"/moral of a country)
Successfull battles lift moral?
Nations like Britian would have the advantage of colonies - but equally would need to import food/materials from the sea (Germany develops subs). America would start of with less experience and influence (far from the battle field) - but stronger economy and longer to prepare for battle.
Decide to work with/against other emipres (German, British, American, Japanese, Russia).
The main advantage I'd see from this over Gal Civ 2 would be that it's easier to pick up on the strengths and identities of the different 'players' (e.g. nations).
Aside from "humans" I don't really know/understand/care what the different races in GalCiv are called. I play the same way against all of them and win. With a WW2 sim the differences would be much more marked - making gameplay more varied. The AI would need to work on creating some balance - but some nations should start with advantages over others.
There could be several scenarios to play - mimicking different stages of the war. The technologies etc should truly - respectfully - reflect what went on however - no more re-writing of history by anyone (see the movie about the "americans" who captured the Enigma machine - it actually British forces that did it). Not to mention the Allies focus on America and Britian - when Russia probably had more to do with Germany's final surrender.
There would be leeway for different outcomes. E.g. Britain keeps Chamberlain as PM(who wanted a peace agreement with Germany), Japan doesn't attack America (America stays out of the war for longer), etc. Even minor things make a huge difference - if the UK (Britain) hadn't researched and discovered Radar the Battle of Britain would have been lost.
There are plenty of docuemtns etc showing technologies that didn't make it into production - these could be added to the game.
Nations such as Italy effectively changed sides close to the end of the War in Europe. What would happen if they hadn't? Or if the War in Africa had went a different way?
I think that certain countries should behave in a realistic way - e.g. Japan would resist surrendering and its troops fight to the death almost always - regardless of what technologies/alliances they had developed. Nonetheless that's not to say that there couldn't be huge changes - e.g. if the US had removed the trade embargos Japan may not have attacked - perhaps remained nutreal or even join in the allies (assuming the allies joing forces in the game).
I think such a game would be fantastic and educational (well - in terms of the consquences of making right and wrong decisions).
Giving that nations would start with very different technologies - more would need to be made of monitoring your foes/allies activities.
E.g. an alert would be shown to Germany when the UK attacked with its first Spitfire. If you played the UK you'd get an alert that Germany had begun sinking ships using an underwater vechicle. Only spies would alert you to Radar - or Germanys first misile (before it was launched). You'd then need to devise a solution or factor in losses.
UK and America created the first atomic bomb (tested on American soil away from potential spies). What would have happened if Germany had got there first? And if the war went on for longer?
There are some aspects however (concentration camps) that I think should be left out if your playing Germany.