Oh, I have a ton of campaigns I want to do. These are some of the front runners;
Become high king of Ireland as one of the Ua Niall Noígíallach and take the "historical" nine hostages of their ancestor.
Norse merchant republic on Iceland.
Win a crusade and play as the kingdom of Jerusalem.
Norse reformation as Erik the Heathen.
Reunite Al-Andalus as one of the taifa kingdoms.
Start as the Roman emperor and create a powerful "barbarian" governor in a border province, then play as him and take over the empire.
But right now the one I'm most excited to try is creating a dynasty of elephant-men and emerge from the jungles of India to conquer the world. Or at least India and Persia.