I'll get a little bit tangential here to talk about what it means to be accurate in a game.
When games portray history as simulation, their underlying intent is really to construct a "computable model of history", which represents a form of historiography. This is so because games are entangled in philosophy: because you have rules and goals that guide player actions, players end up making value judgments about what things are "good" strategies in the context of the game, vs. which things don't matter at all.
For example, because Simcity models crime, the designers of Simcity also have to make a statement about why crime occurs, what influences it, what its costs on the city are, etc. And if you were the designer of Simcity, you might incorporate different assumptions about crime and what its factors are, even after reading a lot of material on the subject. You might even decide to model crime as being beneficial in certain ways. And this decision doesn't occur in objective isolation - if crime affects more things, then it weighs itself more on the player's mind. Or you could eliminate crime altogether and bury it in a different model of happiness or civil order.
Likewise, in sports games like Madden NFL where a roster of sports stars is presented to the player, the designers have to interpret each player and assign them stats. The stats are all funny numbers and can't possibly portray how a human being actually functions in playing sports, but we take them as "believable" based on our collective understanding of what that person is capable of.
Because of this, when a game includes a huge quantity of variables and source material in its simulation, as in Paradox sims like Crusader Kings, that doesn't tell us anything about its accuracy. It makes the portrayal more detailed, but it's still based on assumptions about what's important and worth conveying to the player, and what gets blotted out into a simple assumption or a token representation, if not entirely erased. We can point to simple factual errors like transposing people or technology to the wrong time and place, but those aren't really the interesting part of discussing how games interpret history.
With many games of this type(Paradox sims among them) the biases lean towards a Great Man interpretation, where leaders and their political and military dealings take precedence over other aspects of society. Besides being a familiar trope from the era of pre-computerized wargaming, this convention provides a plausible entry point for the game mechanic - you get to control the leadership in some god-like fashion, usually heavily inaccurate to how an actual leader would have to do their duties - and the goals of the leader generally align with the goals of the player, in terms of gaining more power and defeating enemies. It all works out to a neat scorecard at the end of the game measuring just how badass you were, based on the assumption that being a badass is important and the only thing that matters.
One way in which Crusader Kings differs a little from the convention is in how the player sits a little bit outside the structure of being a single leader, but rather is managing an entire dynasty. In this aspect the game's viewpoint is particularly focused on internal power struggles of the medieval era, but it's not going to give you the depth that you would have if it were a game about a single leader at a particular time. That's where I am going to leave off because I don't have enough experience with either the game or the time period to make further remarks.
Not very. CK2 uses a simple assumption system for most political quandaries (e.g. if you can't declare war on it, murder it or plot on it, its basically impossible to get).
Another thing to note, is that while the Spymaster is invaluable in CK2, there is very little in terms of evidence showing that the role had even existed, besides a few examples that were formed out of necessity rather than anticipation.
I could go into fine detail on the various features (Reliable tax income? Killing the heir to the same family, being found out once, and then continuing to do it without any penalty on further murderings? Levy armies teleporting from one side of the map, to the other, merely because a lord happens to hold land in England and in India?), but to do it any justice would require many paragraphs.
Basically the game requires suspension of disbelief and imagination, which is not valid in any historical context I feel. The game gets basic 'feudal' concepts, and then does not impose cultural or ethnic differences, as the engine can't exactly support such a feature. The differences between say the Lotharingia faction and the Italy faction is mainly the names, the values ascertained to the cultures (for events and decisions) and the income from each province. Every nation runs the same way, with the same eerie efficiency and while fun, is not historically accurate to say the least.
u/3fox did a great job explaining the historical limitations of creating wargames and how CK2 is a proponent of the great-man theory of history. That said, I'm a huge fan of CK2 and am in the process of trying to get Paradox to expand into Tibet.
What I love about CK2 is just walking around the map. Recently I was reading "Four Queens" by Nancy Goldstone. Her book, for all its merits, has horrible maps. So while reading I booted up CK2 and not only had access to a detailed and interactive map of Europe, but also the leaders of those counties, duchies, kingdoms, and empires, and how they dynastically intertwined. PI employs an army of historians to make sure they get a lot of these dynasties and their connections right. There are areas where they cheat and just make up names (the Russian steppe at the 867 start is one area where they had to put in a lot of random chiefs and counts since there's not a whole lot of records to specifically nail down a chief or ruler, another area is Iceland which didn't have human beings in 867, but the game engine didn't support a "No Player" slot in Iceland, so they just put a couple random vikings there). But overall, I'd estimate that they're at least 75% accurate as far as the historical characters are concerned despite that those historians must have some interesting debates in the PI studios to determine how to rank this character or that character's traits and stats.
Sometimes, though, CK2 irks me. I'm not a historian, but I love reading about the central Asian nomads. The fact that PI thinks "Genghis" was his name and not a title and keeps trying to name my Mongol children "Genghis" irks the fuck out of me. Chinggis Khan's name was "Temujin." So PI's weird system would render his name Khagan Temujin of the Mongol Khaganate. Which at least makes more sense than the stupidly sounding and incredibly inaccurate "Khagan Genghis." "Chinggis Khan" simply means "King of the World." "Khagan Genghis" means... well it certainly doesn't translate to the Mongols. So there are times like that where I just want to shake my head. How could they get his name so horribly horribly wrong, but know that his daughter-in-law was a Nestorian Christian? Massive oversight?
This question is pretty vague, but you could start off with some good answers to similar questions;
Was there anything specifically you wanted to know?
reading the thread on how "feudalism" never existed - it is anachronistically applied to a set of heterogenous systems - is showing me that CK2 is a lot less accurate than I thought it was.
I'm afraid I'm not familiar with the game Crusader Kings 2. Assuming I am not an n of 1, would you mind giving a little more detail about how it portrays medieval Europe and India?
The optimal strategy, as far as I can tell involves pausing the game when you start, enacting a dictatorship, murdering your entire court, and then inviting talented people from around the world to join you, who will do so willingly because word of your murders never spreads outside your court.
These people join you because you tell them that you will press their claims to lands overseas, but you never do, and they don't mind.
You then unpause the game and enact a breeding program for your noble house. Genius milkmaid in India? Invite her to Dublin and marry your heir. Your heir is an inbred idiot with hemophilia and the Hapsburg Lip (OK, that part is accurate)? Marry him matrilinearly into the Bourbons and sabotage their gene pool - and gain tons of points for it. The game is scored, after all, by how many provinces your descendants rule.
So overall... no.
But bits and pieces feel pretty good to me, like the Pope calling a crusade, or a Norse chieftain sending out word that he will be going Viking next year and gathering a massive force.
I think Paradox's games do teach a nice lesson though, that history isn't necessarily set in stone. They may follow patterns but there a ridiculous amount of factors. Besides that I wouldn't recommend it to learn history lol.