The biggest thing that bothers me about this game is the stupid way your vassals and other AI characters behave.
Why does a one province count think he can get away with becoming independent from a huge nation like France? What would be nice is, if he's unhappy with your rule or just ambitious, he'd try to make an alliance with other unhappy vassals or even rival kings, and then try to break away. Perhaps if he has the "insane" attribute, he might try to go it alone; right now, they play as if they're all insane. It just gets old watching weak vassals try to break away from powerful kingdoms, over and over and over. And they don't care that every time they tried it in the past, they ended up in the oubliette.
One game, I had a niece who had a weak claim on Hungary, so I had a long and expensive war against Hungary to put her on the throne. Then, when a couple of Hungarian duchies tried to break away, I helped her put them down. How does she pay me back? I think you can see where this is going. When one of my duchies tried to become independent, for some reason she supported my disloyal vassal. Even with Hungary's help, this vassal had no chance in hell of winning a war against my huge empire. After I kick both their asses, my deceitful niece acts as if nothing happened, and wants me to help her put down more of her disloyal vassals.