This game ist awsome. In my game, the AI was pretty good, especially on the right side of my castle. The archers went out hunhting during daytime collecting gold for me and alligned perfectly near the tower each night and fight the trolls off with ease. Unfortunatly, their comrades on the left side of the castle were not so clever, abondoning the outer wall completely except for one or two lonely dudes. Builders would rush in trying to repair the wall and die instantly.
I was at day 15 or something when things startet to get a bit boring. The trollhordes were not increasing in difficulty anymore, as they usually got so big that the night was over before they got to my castle and ran away.
Maybe you could add an ending screen after a certain amount of days, something like "And then the King and his people lived happily ever after etc.", so the player can actually win this game :)