If you compare CK3 with a typical 4X game like Civilization, the main difference is that in Civilization you play the same ruler throughout the length of one game, while in CK3 you play a dynasty. Thus your ruler ages and dies, an heir takes over, and that heir will have different stats and character traits than his predecessor. Not only that, but you only get primogeniture in the late medieval period, which means that for hundreds of years each time your ruler dies, his titles are divided between his children. That is a bit nasty, because not having an heir of your dynasty is a game loss condition, but having too many children will seriously weaken your realm at the death of your ruler. On the map your realm will still be the same, but your counties go from direct control to being controlled by vassals, who will be your siblings. And your vassals can be up to all sorts of shenanigans, and might try to become independent.

That is where the game sometimes plays more like a procedurally generated role-playing game. Frequently you will be faced with random events on which you need to take a decision. And your characters stats and traits influence this, e.g. a character with high diplomacy stats will be more likely to succeed in a decision that includes a diplomacy challenge, or you get "stress" for taking a decision which is against your character traits. Life and death can be a bit random, so in one coop multi-player game my first ruler died very shortly into the game in a hunting accident, and the heir I had to play was just 3 years old, which put me at a massive disadvantage compared to my friends who had far more actions available playing as adult rulers. In another game my ruler became melancholic, and acquired the decision option to try to commit suicide. If you manage to think of the game as RPG, this stuff is interesting and fun. If you only think of it as a 4X, this feels like annoying random setbacks.

One thing I found quite interesting is how much the game changes if you play a realm in a very different corner of the world. Different cultures have different laws, which affect gameplay a lot. For example vikings and Eastern European tribes can go on raids, while Western European realms cannot. Western European realms pay men-at-arms with gold, while Eastern European pay them with prestige, which completely changes the economic conditions. And of course you can play CK3 at 4 different levels of realm: Count, Duke, King, or Emperor, with bigger realms playing in a far more indirect way, with more vassals.

Some of the systems in the game are a bit weirdly balanced, for example the economy. In the tutorial you start as a Petty King (Duke level) with 1,000 gold to your name. In the regular game, even at low difficulty level, a Duke often starts the game with less than 50 gold, and earning maybe 1 gold per month. Building a single farm costs 150 gold, takes 3 years, and adds only 0.5 gold per month to your income, thus taking 300 months or 25 years just to get your investment back. But if you invest your money for the long term that way, you don't have the cash to hire knights, pay for men-at-arms or warfare in general, or make decisions like going on a hunt or celebrating a feast. As a result, in a regular game, you rarely actually build anything. I am currently playing one game using the built-in "debug" cheat mode just to see how the game changes if you have a lot of money, and it basically breaks the game. I'm using the money to buy buildings and am getting slowly more powerful that way; but I could have just hired mercenaries and conquered a kingdom in a fraction of the time. I might one day use that to win a crusade, which otherwise seem to rarely succeed, but I've read that the crusade system is also somewhat broken.

Other game systems aren't exactly broken, but still feel very different from your experience in other games. There is a sort of a tech tree, but only the head of a culture has some minor influence on it, and technologies take decades to centuries to evolve. So technology is more something that "happens", rather than you feeling in control of it. There is a much faster personal skill tree system, but it is tied to your individual ruler, so every time your ruler dies, you have to start over from scratch (or, more commonly, try a different skill tree).

The part of the game that many people will be most interested in, combat, is also sometimes behaving strangely. AI armies move in weird ways, and often behave like slippery eels, constantly evading an engagement. Once you beat them, they only lose a part of their soldiers, and run away again. Splitting up your army makes it easier to catch a small enemy army, but with the risk of you getting caught out by a larger army. I participated in two crusades now, both lost because the AI of the Arab countries managed to bundle up their armies very well, while the crusaders couldn't coordinate at all. Probably working as intended. Compared with the other systems in the game, waging war is a relatively fast system, because a few months of siege is still fast in a game spanning centuries. Again there are significant differences between regions, because in Western Europe you need a lot of time and gold to fabricate a Casus Belli before you can capture a neighboring county, while in some other places you are always allowed to conquer neighbors.

Overall I am having fun with Crusader Kings III, and between the tutorial and some YouTube videos it was easy enough to learn how to play the game. The difference in gameplay in different regions results in good replayability. However, I can't really say that I have gotten into the flow of the game, and I suspect there simply isn't one. To some extent it is more a toy than a game, you mess around and have fun seeing what happens, rather than conquering the world. I played multi-player with voice chat over Discord, and most of our conversation was laughing about the horrible stuff that randomly happened to us, rather that strategizing. If you can get it for free on Xbox Game Pass for PC, it is certainly worth downloading and trying. I'm not sure I would pay 50 bucks for it on Steam.