Divine Wind is the Fourth Expansion for Europa Universalis III as chosen by the fans. It includes improved gameplay mechanics for the rest of the world with Chinese, Japanese and Mongol additions being added, as well as a few more gameplay improvements and tweaks.
Graphically the game has been given a complete overhaul with visual upgrades taken from Victoria 2. However these upgrades have seen a higher spec graphics card necessary in order to play the game and in return have brought the standards of graphics much more up to date.
There have been some minor interface changes such as the new Peace mechanics which rather than opening a new window allows the player to click the provinces on the map which they seek to take or give. As well as other general fixes to the game mechanics.
The Chinese see a new Internal addition which will see the player having to deal with Internal factions in order to be able achieve their targets. This will add new internal problems to attempt to give some historical depth and prevent China from rapidly expanding externally. The new factions give plays limits, as each faction controls certain functions such as the ability to declare war and the ability to colonize. Capable players able to balance the factions well can turn the might of the nation where necessary.
Japan have a Shogunate feature added, with 4 separate Shogun factions being added to the Islands each attempting to gain complete control. The play needs to attain dominance over the other nations through war and even peace in order to unite Japan and join the rest of the world. This gives the player much to do with Japan in the first century or two.
Hordes have a new government system, the main addition simply being rather than being at default Peace with the world they are now at war with their neighbors. They can be colonized and conquered by civilized nations. The hordes attempt to historically model the nations as they were in the past and mostly feature in Europe-Asia.
The buildings system was massively overhauled with many new buildings and new tiers based on technology as well as checks on what the player can build, such as only one different tech 5 and 6 building per province. This also prevents players from building all of there provinces up to there potential very easily and provides more difficulties but more rewards at the same time.
Divine Wind also introduced the idea of achievements to Paradox Games through Paradox Connect. It featured 50 different achievements, some general and some given for doing certain aspects as a nation. The hardest being the conquest of the world as the hardest nation in the game down to the easy monopolizing a center of trade for the first time.
Divine Wind is probably the last expansion for Europa Universalis III. However, this was also supposed to be the case with Heir to the Throne, so it's not totally unlikely we'll see another expansion if the fans demand it.