Just making sure that AI keeps sizeable garrison on cities, disabling auto resolve for seige, passive AI bug fix, suicidal general AI fix and AI not foolishly storming the castle with 50/50ish odd (should just besige and wait for reinforcement) would make the campaign a LOT harder.
And these are mainly just fixes
I think this game needs more fixes, not more scripted challenges to cover up some major bugs with the AI atm.
BTW I remember RTW had the general's viewpoint camera and.... it was TERRIBLE.