It's easy. Because it's the only game on this list that's about sex and politics.
Most others are about killing. And don't get me wrong, as head of a medieval dynasty, there will be the blood of thousands on your hands when your game is done.
But in Crusader Kings II, unlike most other games—its strategy brethren especially—the wholesale murder of your enemies is but a sideshow. A diversion. The hammer you break out when all other approaches to victory have failed.
This is a game that, at first glance—and I'm extending that time period out to your first 2-4 hours with it—seems like a cold, number-driven strategy game. Something only grognards can enjoy, in between tabletop wargame sessions and forum arguments over the finer points of Napoleon's invasion of Russia.
And to be fair to first glances, it is. This is a Paradox grand strategy game, one that doesn't just crunch numbers, it grinds them to dust, sprinkles them across 11,715 buttons and menu options and feasts on them. It's an intimidating game to come to grips with, in no small part because Paradox are so terrible at tutorials, and almost as bad at creating intuitive user interfaces.
Stick with it, though, and my. Oh my. What begins as a blind exercise in clicking things and getting your ass kicked all over Europe slowly begins to blossom. You start to realise what those little "lustful" and "deceitful" character traits on every character mean. You realise that the marriage system is an entire mechanic built into the game, not some pointless piece of window dressing. It clicks that, outside you own little fiefdom, the game is populated by every single noble, religious figure and courtier across Europe (and most of the Middle East).
In short, you realise that this isn't a game about war, or empires, or money, or some pre-anointed goal you must achieve to be the "winner".
It's a game about people. And the relationships between them.
You don't play Crusader Kings II as some disembodied hand, guiding the fate of a people. You play as, literally, a character within the world, part of a medieval dynasty. You can marry. Have kids. Send them off to be educated. Educate them yourself. Choose your own council. Assassinate people. Arrest people. Chop the head off the people you arrested. Arrest their kids, who revolt after you chopped their father's head off. Ask the Pope to excommunicate them. Arrange your kid's marriages. You can even invite people over for dinner.
Every time you do one of these things, your relationships with people change, sometimes for the better, sometimes for the worse. They'll remember your past betrayals, and respect your past achievements. So aside from juggling the economy and the military of a Kingdom, you'll be spending as much (if not more) of your time juggling politics.
And it's amazing. It's not until you're knee-deep in ass-kissing and horse-trading (well, daughter-trading) that you realise, in all likelihood, you've never done something like this before. At least not something like this that works. And it really does work. Sure, it's based on numbers—quite literally, with each character screen giving you two numerical values, one reflecting another's opinion of you, the other, your opinion of them—but those numbers are just the game's way of communicating the complexity of the relationships, and you soon overlook them, reading past the values and seeing the overall feelings and sentiments driving them.
From the mightiest empire to the lowliest county, you'll need to keep tabs on those closest to you, lest someone sneak in one night and poison you. Or stab you. Either or. If they do, well, it's game over.
Oh, wait, it's not. Because this is Crusader Kings II we're talking about here, and it's smarter than that.
When I said you're playing as part of a dynasty, that was only partially true. You are, but you're actually in control of the dynasty itself. So when your first character dies, provided they have a dynastic heir—whether that be a child or close family member—you take over as them, assuming control of not only a new character, but all their own personality traits, history, family and, most important of all, relationships.
Say you're the King of England. You're loved in all corners of the land. But then, one day, you fall from your horse and are suddenly killed. Your son takes over, you think everything is gravy, but then... oh dear. Turns out your son is a homosexual, something jealous enemies can blackmail him (well, you, now) over. You're a coward. A weak ruler. Your wife, probably because of the whole sexual orientation thing, won't give you heirs.
Before you know it, a once-happy Kingdom is in turmoil as power-hungry nobles attempt to overthrow you. You scrape your armies together, begin to crush the rebellion, advance on the final enemy, and then... you're killed on the battlefield. Your combat statistics weren't as good as your dad's, you see. You take control of your sole heir (who you suspected was someone else's kid anyway, since he was born while you were off fighting), a kid whose regent is even more incompetent than the last King, and before you know it, the throne is lost. You've gone from control of one of the mightiest Kingdoms in Europe to lording it over a few crummy towns.
This should be game over. Or at least the point where you chuck it in, realising that there's no hope of victory from here. Only... remember, there is no victory. And there's 400 years of history to play through. It's entirely possible—and I know, because I've done it—to go from a King to a nobody and back to a King again in a few hundred years, courtesy of a slow and methodical game of revenge, of marrying the right people, cutting the right people's throats, climbing your way slowly up the ladder of political power.
That scenario I just described? With heroism, tragedy, intrigue and scandal? It's just one story. From one game. In a complete playthrough of 400 years of European history, from the Norman invasion of England through to the 15th century, you'll encounter dozens more. Start your next game, even if it's in the exact same place, and it'll be a whole new experience. Start it somewhere else on the map and it'll be even more different still.
My favourite games of all time are normally those where I'm given the tools to craft my own narrative. Where the progression of a game creates tyrants, allies and everyone in between. It's why I love games like Civilization and the Total War series.
But I've never played a game that lets me revel in my own stories quite like this one. It doesn't just paint in broad brush strokes, dealing with matters on a national (or global) level. Because of the emphasis on characters, and the wonderful way it implements them, you're playing through full-blown epic tales, which don't just deal with the rise and fall of empires, but all the sex, love, friendship and betrayal that's driving them.
In my review of the game earlier this year, I said " It's like being the Game of Thrones". Which is about the best way I can sum up my experience playing it. Those books (and accompanying TV show) are so popular because they marry the big picture with the small. The clashes of armies are just as important as clashes in the court or the bedroom, and by pinning a grand strategy game on your relationships with people, Crusader Kings II does just as good a job as George R R Martin has. Even if Paradox's game doesn't have any dragons.