The only thing currently pissing me off about CK2 is the plotting. There's just too much of that. For example last night my grandson had his father and myself killed via poison. And since he got caught, pretty much the whole damn country was about to rebel when he got the Kingdom to rule. Seriously, I can understand poisoning his father (in some twisted way), but why poison a 50 something grandfather who would be dead in few years anyways, just to make your progress to the throne faster.
Also I still don't understand how sometimes the areas I control, don't get inherited by my heir. I lost two out of three of the areas I've been upgrading in that even though I have the "eldest son inherits it all" rule in my realm. Is there a limit of how much he can inherit or why did he not inherit some of the areas that were already in his name!