Crusader Kings 2 is one of if not the best game from Paradox if you have the money for all the DLCs.

I prefer ck2 to EU4 or HOI4 because in Ck2 there is roleplaying and a story that you write, and that is something that is not in EU4 or any other Paradox games.

Also the mods are great, if you want to see some "quality" mods check loverslab that has the best mods for this game in the whole world.

Also CK2 has always changing difficulty, not like in EU4 where its always France and the Ottomans who will become the huge blob, here its different.

Like when I did the 7 century achivement run I ended up seeing a medieval great war between the reformed africans and me as a reformed soumonesko pagan fighting against eachother in the middle of Poland, while the remaning Christians were doing religious battle royal on the British isle.

The only 2 downside for this game is that very late game it runs like ♥♥♥♥, the Black Death would help your performance by killing off a lot of people, but if you play a long game most of the world has built good hospitals.

And the main issue is the DLC, there are too much, but luckily they go on a sale pretty often and if you play multiplayer only the host needs to have them all.