For me it's more the feeling of the graphics being quite inconsistent, some of the Imperial cities and especially inside keeps looks great. But then some Vlandian scenes looks like someone played around with default lightning and no post-processing in Unity (honestly they don't even look THAT much better than say some of Viking Conquest scenes). Also I feel they didn't utilize their own character creator probably for the NPC's, pretty much all of them look super weird which certainly doesn't add to the immersion.
All that being said atleast now with the number of sold copies of Bannerlord they have the funding to take this to the next level.