Many fine improvements.
It will take a little, getting used to the way the UI pop-ups work, but I simply adjusted the two Window Lock sliders in the settings to a cozy spot and it's fine. Tons of relevant info in those pop-ups so I used them often.
I have only a few suggestions for UI improvements, but it's a minor thing considering how long my gaming stretches have been. Don't even notice the time, or lack of sleep, go by. Mister sandman can suck it.

I don't recall the last time I got sucked into such long sessions.
Battletech has probably been the closest in recent years.
There's definitely extra learning curve. Even for those familiar with CK2. I mean.. if you prefer to dig into all the nooks and crannies of the mechanics like I do. Some people don't care so much.
Most everything was improved some way. There are more checks on quick blobbing, but they're not hard limits for the most part. It gets a 'Foak-yayah!' from me after a bit under 20 hours. Been taking some beatings and lovin' it. Just makes me wanna come back for the challenge in expanding everything.
Being how it is on release, I only see good things in the future.

If they don't try to jam too much junk into the gears past a certain point, as happened with CK2.