Just bought it - to play a mod, paradoxically enough.
Which one?
Elder Kings 2. I am not that interested in CK3 itself as Paradox games usually remain unfinished for about 7-8 years while they're working on DLCs. It seemed EK2 was more popular than Elder Kings 1 and much beloved. I recently got into Elder Kings 1 in CK2, and it got me on a TES lore spree, just like Geheimnisnacht earlier got me on a Warhammer lore spree. It was so cozy and reasonable. But it turns out it has a fatal flaw. They added a ton of useless small buildings. This was only a minor issue in the original CK2 or other mods like After the End or Geheimnisnacht. But here if you have, say, 15 holdings, then you need to go to every holding and build every 40 Gold building manually. Given that there are about 5-7 times as many buildings, this renders the mod unplayable once you have enough money.
The autobuild mod for EK1 doesn't work as they had stopped updating it shortly before EK1 stopped getting updates, so they're incompatible.
I feel rather let down by both of those things (the absence of ledgers in CK3 and the building fiasco in EK1). I'm done with EK1, but I'll try to persevere and give EK2 a run. It's just somehow very sad that good things like ledgers must get removed. So much effort undermined by those inexplicable dumb decisions, and the change is in all the wrong directions. The whole interface looks trashy, like it has twice as little info with twice as much clicking around. Paradox games are first and foremost interface games, so it's very painful. This is again quite sad as the other new Paradox games like Stellaris and Imperator: Rome have a fairly sleek interface (despite some glaring errors like the absence of a convenient way to move pops in I:R).
Always wild how divisive the CK2 vs CK3 interface debate is. Many people think the CK3 interfact sucks and then many claim CK2 was unplayable compared to the CK3 interface.
CK3 lacks basic and obvious functionality. For example, why on earth did they remove the "will accept invitation" filter, so that now you have to click every character. Why do I need to zoom in so much to select counties (although there is a functional realm menu). There are all sorts of weird minor decisions as well, like inexplicably placing the icons slightly to the right of the column for which they are responsible. A lot of this seems aimed at artificially prolonging game time. Some of it also relies on mods for basic functionality. For example, there is bizarrely no terrain map in the game and you need to download a mod for it. For some reason, there is no income map. There are industrial amounts of empty interface space but things like map modes are hidden behind a plus button. Of course, the mods stop working any time an update happens, and then they get updated at a different rate, so it's impossible to get them working all at once.
There are a few things that aren't as bad as they seemed though. The 3D portraits are a bit of a downgrade compared to the late CK2 portraits (after all the DLCs), but they are disarmingly cute.
To be honest, I think that's it for me as Paradox games go, like Mass Effect was for Bioware. I also checked the main game, and they made Finns, Estonians, Merya, etc. into Asians. What a bunch of assholes.