Like the ledger, most rule changes, rivals/friends, etc. Could use some of the tweaks people mention.
I started as Byzantium and was having trouble just holding it together as the ruler starts with horrific stats. I had Elective Law, and when he died, it wasn't his kin who inherited, so I became a count (his son) even though first in line to inherit did get Emperor. So I saved and reloaded as him. Only problem is that all the court was lost, so now I have very few - only enough now to put one in each advisor slot. Think we may need a bit more advisors.
I'd like to actually be able to get popups or whatever when techs are gained (as an option).
About 10 years in, and Germany has crumbled, England also. Yet Wales has almost been formed as the AI gets easy vassalization (I can't seem to get anyone to vassalize with me, even though relations are +150 or so and they are 1 province while I'm the Byzantines).
The first time I tried, the Seljuks were destroying me as I didn't have the money to fight them - all kinds of corruption in my demesne provinces !? And with lousy stats. And I messed up by changing a law early.

So I reloaded, Seljuks made early peace for money, and now as I have rebellious vassals, I spend all my time and most of my money just to keep it all together.
Seems almost no one in my family or court to marry...? I keep getting offers for my one good advisor, and I'd rather marry her to someone in my court to stop that, but while there are single men, none are my family, so I can't arrange a marriage...
One question - I have a vassal with Loyalist, but it gives no loyalty bonus??? He was sliding to rebellion based on my traits. Understandable, but a Loyalist who will do almost anything for his liege should get a loyalty bonus.
I'm interested to play more. Religious war keeps down the overruns, though if it gives BB, that isn't so good.
I really like the peace option to allow for reinstatement of the vassal with full or reduced status. I've used it a couple times because I can't afford to lose courtiers by giving them count titles, and my children are too young for them. So I've kept the Prince titles I won in the war and gave back a count status to the rebellious one. Seems a fair enough trade and doesn't hit BB too much.
For some reason, the base tax of Byzantium declines over time. And it's not because of Poor land or other reasons. I have stewardship now at +146%, yet it keeps declining. Why is that? Is it the thieves guild or whatever? Or is there another reason? How do I stop it & even hopefully make it grow?
Overall, it's great. I'm definitely going to be playing a lot of CK/DV over the next few weeks.