This new trailer for the upcoming Crusader Kings II: The Old Gods gives a taste of how you'll build a pagan empire, beginning in 867 AD. The base game was one of Kotaku's 2012 Game of the Year nominations; the expansion will be out at the end of May.
One of the great things about this expansion (beyond the obvious) is being able to play Pagans in the existing timeline. There's only one start date for the expansion, 867AD, but pagan religions were still alive and, for awhile, growing during the time of the Kublai Khan. This essentially means that the entire map is now open for play, except for theocracies such as the Papacy and the Teutonic Order, as well as the singular Islamic orders, such as the Hassassins etc.
Also of note is that while the expansion is technically built around allowing the player to be one of the Viking lords of the time (war parties, raiding parties, longboats etc.), the game introduces unique elements to every pagan religion in the base timeline and the new timeline, which will add... So, so much replay value.
Can't wait, man.