Alright, I'm roughly 300 turns in, playing on one of the higher difficulties (don't remember which one exactly), featuring the Grand Campaign scenario with Debeurath march. I took that little thing and first reformed as Wales, then went on to conquer Ireland and England, and am just about to take over Scotland too for good measure.
The game's central resource is definitely Authority, and you'll likely see your early and even midgame revolve entirely around it, especially if you play a tiny nation like I did. What Authority is is basically a control switch for all the anti-blobbing mechanics the game has. Have high authority? Anti-blobbing gets turned off. Have it low? Get ready for your realm to fall apart. It actually works and does slow any map-painters down massively in that expanding over your domain limit costs authority each turn, and the only reliable way to raise it is to build some high-tier buildings (and be in top 10 most pious nations, if you can). This means that if you want to play well, you can't just conquer shit, but also build your regions up – not only is playing tall fully viable, it's actually kind of mandatory, as you need to build tall first to play wide later (though that's less of an issue if you start with a country that already has most of the reforms behind it, I imagine).
On that note, building stuff is kinda fun. There's lots of different building chains for everything, and the building options get randomized (though you can decide to pick manually if you're willing to take an authority hit), which keeps things from getting too repetitive. Sadly, I found resources other than Authority to be so easy to amass as to not really be an issue ever, which drained a lot of the fun from the system – usually, I just tried balacing piety and health on the local level (as being low in either causes problems in the province), while aiming for authority-raising buildings whenever I could. Also, AI is kinda garbage at this – I always see their regional development horribly stunted. As a result, it's not difficult to be one of the most pious nations even as a tiny country, or to start amassing legacy (ie. victory points) at a mass scale while being just a smudge on the map, simply because you're the only one utilizing your lands to their full capacity.
Militarily, I saw the AI as being reasonably competent (it can launch successful campaigns against its enemies and conquer territory, even if not nearly as efficiently as a player would), but its failings in the economy area cripple it quite a bit. They just get curbstomped by your doomstacks. Come to think of it, that may be the reason why resources feel too abundant – I never really had to build my army up as much as possible, because my opponents didn't require it – two doomstacks striking out of Wales was enough to conquer all of England without even a hint of difficulty. A definite shame – I hope they improve this aspect of the AI in the future.
Flavor-wise, there isn't much in terms of writing, but I appreciate that your country name can change (depending on your origins and conquers, ie. Debeurath->Wales, etc.) and that there's tons of unique units for each area of the world. You also get different building chains depending on your religion (and sometimes even on your culture).
Overall, it's pretty fun, though a bit of a diamond in the rough.
edieval, right?
