The Conclave DLC expands the Council system in game, giving you more control over how your nation is governed, adds a few new mechanic and reworks some others.
+The council mechanic is improved greatly. Powerful vassals will want a seat on the council and you have to decide between if you want someone competent to be in your council or an incompetent but powerful vassal. If you put the competent person there well he'll get his tasks done effectively but your powerful vassal might get annoyed, start planning things behind your back. If you put the powerful vassal there you won't be risking a civil war but you will have to cope with your Empire being run by idiots that can't handle the simplest tasks.
+Characters can owe you favors now and you can owe others favors as well. This can really force your hand and get you into situations you didn't really wanna be in and you can do the same for others too.
+Reworked laws.
+You can create a mercenery band of your own now but you can't really lead it.
+Diplomacy system has been changed a little, making it harder to get alliances because they have to be built on top of non-aggression pacts.
+Changes to the combat mechanics.
+Different death sounds according to several factors like how old was your character, how they died etc. Pretty minor stuff in the background, I wouldn't have even known it was added in a DLC if I hadn't read the wiki but its there and I like it.
+Defensive Pacts, new law screen, some QoL features, some improvements to the factions system...
+A lot of other reviews mention that the older education system for your kids was better and the newer, more luck based system isn't as good. Some others say that the older system was too repetative and took a long time to handle when you had many kids. I like the current, simple, more luck based system where you still have some input.
Pretty good DLC.
izigame.me
It may take some time when the page for viewing is loaded for the first time...