Leviathans gives you many additional options to "build tall". More state and province level options have been added, Monuments, which are historial structures in the world, give unique bonuses for owning repairing/improving them. More options to spend your admin points on infrastructure which gives tons of bonuses and makes building up smaller nations alot more fun in my opinion. If you like more internal management or starting off as smaller nations, would recommend this DLC.

Crusader Kings 3 is a large improvement on many features of crusader kings 2. Better and more clear Genetic traits process during marriage. The new Dynasty additions add alot more detail and depth to running not only your court but your entire bloodline. Combat units and phases are much more clear and they have more details on the units and how to properly use each. While it is lacking some features CK2 had with all the dlc, that is to be expected with Paradoc's game plan but i can say CK3 has alot more available to you at release then ck2 had. Love the New engine they use to, cant wait to see how they use it for their other titles.

Adds more depth to trade, by allowing non merchant governments to use trade routes. also expands on horde nations.