You may have noticed by now that I am a bit of a Paradox fanboy. It's hard not to be when you love grand strategy games, and they happen to make some of the best around.
That said, I can summarize Crusader Kings 2 with a sentence:
"If god didn't want us to conquer the holy land, why did he populate it with infidels?"
As the title says, you will play a Crusader King, (or duke, or count, maybe emperor if you're lucky) in the base game. You must try to carve a dominion for your dynasty within the holy lands -- or anywhere else, really, but the Middle East is pretty rich. You will play as your ruler character until he dies, then continue your game as his heir. This goes on until your dynasty is either toppled and unladed, or fades into obscurity and goes extinct.
The base game itself is good, but the DLCs make it a hundred times better -- allowing you to experience a plethora of fun events and easter eggs, and also giving you a chance to become a filthy pagan, an incestuous zoroastrian, or a Muslim Jew or Buddhist. These expansions even flesh out character interactions, bring the start date backwards in time, and add more realistic illnesses.
The only sore point here is the price. Both the game and most of the DLCs are overpriced at the moment and (in my opinion) should only be bought with a 50% or more discount on Steam. But whenever you do decide to buy, this title will grant thousands of hours of fun.
Get Crusader Kings II on Steam. Deus Vult!