Does this mean that the focus is on families rather than the country, as in CK2? What about CK2 features such as plots or assassinating people, are those in this?
Yes, you play with characters from a dynasty. Since the inheritance law is elective (with preference for your heir), you can even fall from a Clan Leader to a Kokujin (Sengoku's Count)
Sengoku was the game which introduced the Plots feature. However, there is only one kind of plot: to invade a Clan larger than you (you collect allies and your target's vassals with target vassals becoming your subjects when you invade).
Assassination is also there, but you must wait for a Ninja Clan (whom you cat attract with one of your cancellors). Alongside assassinations, they can do kidnapping, dishonoring, etc.
There are some other differences from CK2:
- you can declare war on anyone and the moment you occupy a province, it immediately becomes yours
- your max demesne is always 5
- the game has a goal: you have to conquer 50% of Japan and then hold it for a certain amount f time (the AI will try to stop you from winning). If you survive that you become the Shogun and the game ends
In general, it is a much simpler game than CK2, more oriented on waging wars than diplomacy and intrigue. It makes a good break when you want to play a PI game but don't want anything complex or time consuming. It is unfortunate that PI never released any expansion which meant that much of the game's potential will be undeveloped (luckily, the game is very stable and bug-free (I don't even remember ever encountering a bug) so you won't miss patches)