Heathen nations in CK2
This DLC reawakened my love of Crusader Kings II. The heathen nations which were being weeded out at the time of the base game are now plentiful and - to be honest - more fun to play. What I didn't realize is that this isn't just about playing as a Viking (though that's definitely a fun place to start). There's a whole world of turmoil to plunge into. And, the feel of the game is different than the base game. Other than Sword of Islam, this is one truly essential DLC to flesh out your CK2 experience.