1.The looks-graphics,animations,art and unit design.
2.Far more quality of life changes-left alt,being able to see where your teammates are etc.
3.Extra options for fights.In warband it was attacks and kicks. In bannerlord you have attacks,kicks, shieldbashing, shoving, crouching for dodging.
4.More weapons-it doesn't feel like every faction has the same 2h and 1h+shield combo.
5.Archery-as someone who played mainly archer on siege servers in warband I consider it way better in Bannerlord.
6.Sieges(if they worked lmao)-its not moving up a single ladder or banging a door for 10 minutes like it was in warband. Plus it has actual siege equipment.(that doesn't need a mod to access)