What a great game! I'm now totally in the grip of the "one more turn-syndrome". To bad I have to work for three nights(and sleep during the day) before a can return to it.
Before I get to my suggestions I need some advice or clarefication on one thing. I think I have started to figure out the tactics pretty well but I don't really know how to treat towns and forts that are not objectives or strategic.
Should I ignore them or is there some advanteges that I have missed if you capture and hold one? Well, shelter during winter is one...
wich leads to my first suggestion. It's not very detailed but I hope you don't mind.
During winter there is not much to do and thats fine with me but I was thinking of some sort of information gathering or rumour event that told the player of ,lets say,an enemy fort that's starving or where the militia have gone home and is therefore less garrisoned. It's up to the player to decide if it's worth the risk to march against such a rumoured weak target. Just an idea.
The next is a more serious one

What about a summary screen (or several) at the end of a campaign?
A like statistics

Wich leader died where and when. Who was injured and how many times. Casualty numbers for different kind of troops...and more?
There may be other stuff as well. I have no idea if this is hard to implement or not but I think it could be nice to sit and contemplate this kind of things after a long campaign.