I find EU4 to be the CK2 version of EU3, not only engine-wise but also on the interface-level, and europa universalis is a game of information panels
so it is possible you dont like the changes.
Some changes on the top of my head :
- missions, national ideas, core system, ruler bonuses revisited
- badboy changed for aggressive expansion
- provincial decisions and population factor removed
- taxes-trade-production simplified
- diplomacy overhauled (for me its the best diplomacy system ever now, you should check it)
- more map filters
- over documented ledger (a bit too much... you can disable it entirely in your mp games)
- some changes taken from various competent mods
- ofc graphism
And like Latvian said the MEIOU & taxes mod makes it even cooler.
(MEIOU & taxes = MEIOU + death & taxes, the two "best" mods of EU3 for me)