This game takes a LOT of work to get into. Had the base game for years, tried a couple times to learn it but failed (tutorial sucks btw). What helped me in the end was a 20-hour tutorial by Arumba on Youtube; even then, I still learn something new on every playthrough.

CK2 is all about maintaining and expanding the power of your dynasty using all means necessary; you have to marry the right person, pick the right subordinates and council members, make the right alliances, declare the right wars, and most importantly have the right heir.

I think what fascinates me the most about this game is that every AI action is motivated by a reason, and a HUMAN reason: my neighbor hates me because of different religions, my vassal hates me because of my foreign culture, my brother hates me because I'm the heir to the throne. This, along with annotated historical events, gives you a really good perspective on why things happened in that era.

Cons maybe that it has tons of DLC (I think overall it's the game I spent most money on ever, despite always buying on sale). But the base game itself is already very rich, and every DLC adds a lot of flavor; considering the long-term support for this rather old game, I guess that they may be worth it.