Tried CK3 yesterday.

Overall, it is the same as CK2, but with large console interface for idiots, some improvements like more sophisticated lifestyle/trait system, and some simplifications like removing specific nomad/republic gameplay (surely they'll go into DLC). It is full of 3d, has complex face generator, looks pretty different in style, but still mostly a same game.

I think they made combat somewhat more interesting just by allowing even small countries to have some kind of retinue (although combat as process is less sophisticated now). They also put most of personal-related CK2+DLCs things into base game (swaying, lifestyle). Council is weaker, laws are passed easier, but instead global levy/tax law you'll need to negotiate specific vassal for individual agreement.

Personally I think that game is relatively good, at least at first glance.