Have you tried the Game of Thrones mod for Crusader Kings 2? You should; it's very good inspiring whole tales of intrigue, treachery and incompetence. The mod has this week updated to v0.8, further bolstering an already perfectly playable total conversion with a full Night's Watch overhaul and White Walker rework.
Here are the basic features added in v0.8. You can find a full changelist over at the mod's forum, but be warned: they may contain nuts spoilers.
Many White Walkers improvements/fixes
Night's watch revamp
Titular kingdoms for Essos
Dynamic Golden Company invasions
A new 'Prison Break' event series
Reduced Jon Snow's learning attribute to nothing
Okay, fine, I made that last one up.
Download CK2: Game of Thrones here.