There are basically 3 major scripted quest: The Deluge, False Dimitry and Black Mace for the Polish, Muscovite and Cossack factions. The Swedish and Tartar have the rebel faction in which you can become marshal for the rebels and support the claimant (who becomes the ruler/king). The Deluge and False Dimitry, you can actually become king and have other lords in your faction.
The ultimate is to become a rebel (you can choose any faction), but no lords will ever serve with you, and try to conquer the whole map by yourself.