I've gotten into this game a bit more in the past week. Maybe I made a mistake by choosing to play as the duke of Kent.
Anyway, none of my first 5 rulers made it past age 30, illnesses and a couple of assassinations. Now I'm a duchess because of all the death in my family. Locked in gavelkin succession so I have to perpetually assassinate sons to make sure I only have one heir. yay. I married the duke of York and my heir is now the duke of both... Well, I have to kill one of my sons to make sure it's not all split. What's the point of all these succession systems anyway when the one you really want is primogeniture anyway. It's just like ... an extra challenge to get to primogeniture. Sure, gavelkind gives you the possibility to hold more demesne... woo-ptee-doo.
Also, something's weird in my game... I'm of the same dynasty as the king of England. The Godwin dynasty. So everytime I'm in a situation where I have no children yet, my heir is the King of England (as a sidenote, I had a bastard child with him as a duchess lol). You really have to give yourself the goal to perpetuate your own family, because the consequence to failing to have heirs, and failing to manage your family, is that you actually end up as the king of England. "Oh, your family died there, you failed, here, play as the king of England! Whom you're barely related too because you share the same great great grandfather". It's like the game is telling me "die already and become king!".
Anyway, it's now 1130 or so and I still don't own more territory than when I started because I can't war with my neighbours (vassals of a high crown authority (all attempts to reduce it failed)). So I'm trying through marriage (gonna be duke of York and Kent soon... although I'm sure something will go terribly wrong when that happens).