There are a few things that have stood out to me so far.

Some smaller things:

• Food doesn't rot.
• There are no feasts, which were a good oppurtunity to improve relation with a lord/lady.
• There are less options when camping.

Some bigger things (to me anyway):

• The courtship system was significantly reduced, basically just a few speech checks where you know the exact % chance of failure/sucsess, then purchase them from their highest ranking clan member.
• The npc compainions don't feel as unique as in Warband, and I find myself almost always skipping through their dialogue. Maybe this is just my run but I have only had one instance of a companion taking issue with my actions.
• You can't really start as a nobody anymore. In Warband you could serve as a soldier in someone else's army and work your way up the ladder, it made for a harder path to becoming a vassal and an interesting early game. In Bannerlord you can start as someone who didn't have noble parents, I did, but this part of the game just felt less fleshed out.

I haven't quite started my own kingdom yet, I want to spend some more time as a vassal. But I have heard that kingdom managment and diplomacy feel unfinished to many. I guess I'll have to see this for myself.