EU3, darkest hour and mount&blade are the ones which i played the most next to CK2 and i played all of PI games since EU1, if this helps you anyhow 
Not that I'm an expert in the field, but I'm going to use it to teach my girlfriend basic economics and politics. It is most definitely very historically interesting.I'd say Victoria 2, but only if you have a history/politics/economics interest. It's a lot more modern, with POPs (Portion of Population) dictating the game more than characters (there are very few characters, just some generals get names, and some politicians are mentioned in events).
King of Dragon Pass is a very similar game to CK2. It's a strategy game where you manage a tribe, look after characters, respond to random events etc.
The only other games I have from Paradox are Sengoku (And I have a hard time getting into it. It feels like "CK2 in Japan, but not as good" to me),
It's CK2 light. The only things you do is waging wars and blobbing. Extremely boring after a few hours.