I don't feel at all qualified to do an actual review of this game, completed or not because this game just isn't one that is made to appeal to me at all. It's also something entirely different from any other kind of game I've played, so I have no real bearing on explaining to you how well the mechanics of the game function as I have no real point of comparison. But what I can do is explain to you what this game is before you try it out.
You cannot win or lose Crusader Kings III. You are playing a specific person in the world. Someone who owns a stake of land. You play political games with others trying to win their favor, enacting murder plots, collecting taxes, and you even have a wife and concubines. You can send troops off to war for more territory, but the battles are pretty un-interactive compared to just about any other kind of game. And since you can only directly control so much territory, you set vassals to run certain areas for you, and they may turn treacherous depending on various factors.
The only way to 'lose' if you can even call it loosing, is if you die of old age or murder plot without leaving behind any heirs to your dynasty. Of course, you can just switch who in the world you are controlling at any moment,. The game just ends once you reach a certain year.
You can't call this a strategy game, though that is the kind of game you would think to most associate this with. It's effectively a management game, and what you are managing is the story of the world that unfolds over however many years the game takes place. You don't have 100% control, chance and innate abilities play a part, but you are effectively just guiding along the story until its conclusion, and you can be involved in as many areas of the world as you feel like with the ability to change characters. I honestly thing Simulation is a much better tag for this game than Strategy, but even that isn't entirely right.
That said you can do a lot of things like arrange marriages, take on Concubines, scheme murder plots, and a lot of other things. But while you make all these decisions, it's not as hands-on as I'd like, This is why I am saying you are more in the role of management than anything else. I can see why this would appeal to someone, but it's just not for me. This post is mostly just to highlight what kind of game you are getting in Crusader Kings III.
Also I was able to attempt to seduce my sons wife, so yeah. There are some odd things you can attempt to do in this game.