The King of Strategy Games
Europa Universalis IV, like most Paradox games, has a very steep learning curve. Dipping into the game requires a commitment of time and energy that is unlike other strategic games. It helps if you have a good understanding of history and if you are a history fanatic. If you are willing to spend the energy to learn this game system, you will be rewarded with what may be the best computer simulation of history available.
There are many DLCs for the game but you should not tackle them until you develop a good understanding of the game mechanics. Once you learn the game mechanics of this game you will easy transfer your knowledge to other Paradox games.