From: Santa Rosa, CA
It starts from the WitW engine so it has expanded air and logistics rules. It uses the War in Europe map that was in WitW (but with further work done in the eastern areas to improve it further). The OB started from WitE's OB but with further research and improvements. Basically all data areas are constantly being improved. From this starting point there are may additional changes including big ones like the event system and theater boxes and smaller ones like double and single rail lines on the map. If you have played WitE you will recognize about 50% of the game, and if you've played WitW, you'll recognize another 25% of the game (give or take). Having played both you'll be able to jump in quickly and start playing, but you'll find lots of subtle and not so subtle changes that will impact your strategies. In theory, by using the WiE map, we have the potential for someday having scenarios that include both east and west, although as has been mentioned before, anything before 1943 would require more involved naval rules or treating the Western Front as a Theater Box until 1943.
All understanding comes after the fact.
-- Soren Kierkegaard