All right, so after the weekend I'm 150 years in as Florence-->Tuscany. Overall I'm digging the game and am happy with it. It's not perfect and there's a lots to fix but I can see myself sinking hundreds of hours into it.
Surprisingly I had zero crashes. Out of bugs it's mostly some situations and organisations not working as intended (or could be me not understanding how do they work), ship auto-transport not working at all and the terrain map mode not working (it shows paper map mode instead which I play with 99% of time but still). Despite my CPU not meeting minimal requirements, the performance is OKish. Perfectly playable although slower than my usual playstyle with speed 4-5 and lots of pauses. Actually better then CK3 150 years in despite me meeting recommended requirements. It also has faster load time than EUIV.
I like how they expanded on many of the EUIV mechanics and the stuff they stole off CK and VIC is implemented in an organic way that makes sense. At each step I discover something new about mechanics and I like most of it (for example during a long war with Naples I discovered how much levying most of your peasants while being small, decently urbanised country can fuck up your food stocks and economy). It has nice depth to it and makes a good attempt to simulate some historical aspects of the game. I like pacing of the game and working towards certain goals, like slowly building up your standing. or increasing your power against estates while still trying to squeeze as much benefits of them as you can, feels satisfying.
My two biggest gripes are AI and interface which gets worse the longer you play. In terms of AI, I would be fine if AI would be less efficient in approaching the game mechanics and at some point was just left behind by the players. This what always happened in PDX games. But AI seems really bad even at the most basic activities. It's good at hugboxing the player but lacks a lot in terms of aggression. In my playthrough, Naples hated me since day 1, was much stronger and had better allies but did nothing against me. When they were distracted in Balkans, I used opportunity to grab some land of them in a costly and long fought war. After that they hated me even more, had cores to retake and were still stronger than me and still decided to do nothing, letting me expand in North Italy until I became match for them. Even France, the Ottomans of EUV, seems very lethargic in my game. I think something went wrong with a 100 years war since they keep fighting the same war against England and Castille. England has a little of land left in Normandy and a vassal in Aquitane. France completely mops the floor with them and then peaces out without taking any land. This repeats as soon as truce expires.
Other issue with AI is logistics. I actually like that distant allies don't send the armies overland across the whole Europe, whether it's intended or not. However, AI is much worse in transporting troops with navies than it was in EUIV. In my game Tunis conquered, Sicily, Sardinia and Corsica. I declared war on them. Despite them having stronger navy than I did they hardly sent any forces to oppose me in Corsica and did nothing to defend Corsica and Sicily. They didn't even go after my transport ships, although they could easily sink them (something EUIV AI jumps on as soon as they get a chance). When I later sailed by their coast I've noticed that they stacked 40k levies on the beach just chilling.
Overall, the weak AI means that although the deep mechanics mean that optimising your playthrough is really hard, game remains easy as it does nothing to punish even extremely sub-optimal gameplay (and since it's my first playthrough I did fuck up a lot).
On the topic of UI I can give one example. I wanted to get a cardinal and decided to check tooltip to find out how to do it. So I opened Catholic organisation tab and moused over the word Curia. Than in that tooltip I moused over the word Cardinal and learned I have to build "Seat of Cardinal". I click the link to build it. Can't. I scroll over the province to see that "Requirements not met". So I scroll over that to learn that I need to take decision to request cardinal from pope. How do I do it? No info. I tried the religion tab, tried Catholic organisation skill, tried province menu, tried diplomatic interactions with the Pope. I still have no idea where the option is. Five tooltips in and I have no clue how to do it. I ended up conquering cardinal from Milan and kicked Pope from Italy. He's chilling in his West African colony now. Good riddance.
My most recent annoyance with the UI is building new buildings. Available options keep increasing and and they are all contained in one menu. Technically you can sort them, but for some reason they are sorted by which job is employed in them rather than by category (admin, production, military etc.). This can be annoying since for example goods can be produced by burghers, laborers or peasants and buildings I would define as "admin" can be run by clergy, nobles or burghers.
The game obviously needs a lot of tuning and fixes. Still, it's pretty solid. Easy 8/10 with potential for improvement. I would go as far as to say that even if no new content DLCs were ever to be released, the game would be worth its asking price provided all the jank is fixed.