There are a lot of new game mechanics that give this game a different feel.
The most obvious is the change in land combat so that it lasts for only one round for each player, and it is possible for players to reinforce each other without shooting. (I.E. France invades a territory using tanks and British or American troops follow)
The other major change is the minor allied powers(Serbia, Romania,Belgium, Portugal, Arabia, Albania for the allies and Bulgaria for the Central powers). The allies can choose when to mobilize allied powers, unless they are invaded. They represent free units and income if the allies move a troop into them. The Allies have a much easier time activating these places because they have more transports available.