Hopefully the whole 3 generals things for the battles will add nice flavour : You can have a good trio, with you good martial king, a good Marshall and a highest noble of quality, or you could have a crappy trio with infighting during a regence.
This could emulate well an Agincourt type of situation, where the king wasn't there (crazy) and the seasoned officers (the marshall) got overuled by cocky incompetent dukes (Orleans, Alençon, etc..) who ended up charging like dimwits and causing a complete disaster.
I also hope that the whole war engine will be better. In CK1 you ended up using only your personal demesne soldiers most of the time because : 1 they were usually enough, 2/ you didn't have enough money to finance using your vassals' hosts. Only when the situation got tense did you start using your vassals troop. Hopefully in CK2, if you are at war with more than a rogue duke, you will have to draw on your vassals and you will be able to campaign with them, not go for ultra blitzkrieg before getting bankrupt...