Grand strategy of a medieval scale.
The goal of the game is to accumulate as much prestige points as possible while your dynasty still exists to beat the score of major historical houses. I like this as the objective of the game is not the typical conquer the entire world like in most strategy games. As such you can remain a Count and still "win" per se.
So how do you get prestige? Through many means, marriage to noble houses, throwing feasts, cosying up to the church etc. Warfare is still part of the game but not a major component. War costs lots of money and is best used sparingly. Politics is the main way you will climb the ranks of medieval society.
Through it all, you and your heirs may face sickness, assassinations, imprisonment, bouts of madness and various other ailments. You must ensure you always have a heir to your dynasty or the game will end. Which isn't easy considering some of your sons/daughters will be infertile or die an early death. Some may even rebel against you and usurp your title.
Apart from your heirs, you also must keep your subjects happy. If your a king this means your dukes and counts. As a count your barons. Fail to appease them and they may start a rival faction against you or take up arms.
As you can tell Crusader Kings 2 is an incredibly complex game. Don't expect to master it in a single playthrough or even two. But once you grasp the mechanics, you will be hooked.
For fans of grand strategy, Crusader Kings 2 is in my mind one of the finest entries in the genre out there.