I picked up EUIV over the holidays but haven't played it yet. I bought the save game converter DLC for CK2 with the express purpose of one long continuous game that began in 867 and ends in 1820-something (I forget EUIV's end date).
So far my CK2 game is around the year 1250, I've played it "round robin" style, whenever my character dies, I randomly pick another character to play from that moment on. So far I've played as both an Ethiopian duke and the king of Abyssinia, as king I conquered Nubia and Egypt and formed the Ethiopian Empire, which is still a power to reckon with two hundred years later. I played as the head of the Umayyids in Spain and attempted to push up north of the Pyrenees into southern France, the resulting Crusade was quite successful. And two orders of crusader knights appeared and with the kingdom of Leon have not only completely taken over the Iberian peninsula and reconverted it all to Catholicism, but took advantage of the crumbling Umayyid empire and have taken overeverything from Morocco to Tunis. As the Roman (Byzantine) Emperor I retook land last in southern Italy and Sicily, took over Jerusalem, and pushed north into the Caucasus Mountains, and much of what's directly north of the Black Sea, and helped convert Pagan Ruthenia to Orthodoxy, who in turn converted westward all the way to Poland and the Baltic coast. Presently Orthodox Ruthenia extends all the way into Finland and is at war with the Catholic crusading Teutonic Knights to fight over whether Finland will be Catholic or Orthodox. As Persia I converted to Zoroastrianism and single-handedly revived Zoroastrianism back into the state religion of the Persian Empire.
Currently the Mongols have appeared from the east, the Ilkhanate has swallowed up everything from the Aral Sea to the Euphrates, and to the Persian Gulf, and subsequently converted to Zoroastrianism--so Zoroastrian Mongol hordes. The Golden Horde appeared east of the Urals, spread west and have everything between the Ural mountains to Orthodox Ruthenia and Catholic Russia. Most of that land is either Jewish or Orthodox, so I'm curious to see if or to what religion the Golden Horde will convert to.
I own the Sunset Invasion DLC, so it'll be interesting when the Aztecs appear from the Atlantic and set their swords upon Western Europe. Most of western and central Europe remains embroiled in a family feud going back to Charlemagne; as such the Karling family owns everything from England and Wales to Germany, France, and Aquitaine, to Castille and Carpathia (the unification of the states of Hungary and Bohemia). If they can somehow pull together, they may survive the coming invasion from the West.
Needless to say, this is proving a most interesting game, and I'm quite excited to see it keep going in EUIV.
/nerd
-CryptoLutheran