Surprises me there is no thread for this game yet, nor for it's predecessor. I confess I have never played CK I but I am playing CK II and I am loving it, very unique game. You are not a nation but a dynasty. Or rather just a family and when you pass away you continue playing as your heir. You need to keep this up for as long as possible until you die out.
Gameplay is very diverse in my opinion, you need to deal with your family, personal choices, vassals whining, peasants being the useless rabble they are, etc. etc. while you also need to research technology, build new structures, conquer more lands, destroy infidels, etc. and of course politics. Always marry your daughters to influential dukes/counts/barons and your sons to daughters of influential people. Power is power!
I also bought the Ruler Designer DLC, that's a lot of fun. I created the Duke of Saxony as an alter ego of myself with adjusted names to fit the German medieval situation. Really cool.
And the Game of Thrones mod was released a week or two ago; best thing I have ever played in multiplayer! The fun I had with some friends even equals the fun I had with the 130th in FH2. And that's very hard.
Here a screenshot of my current Duchy of Rostov, my goal is to make the Kingdom of Rus. Currently at 38% of the necessary regions. Will make it to 50%