If you thought of the Warring States era of Japanese history at all, the overriding impression would be of horrifying loss of life, as armies rampaged across the land often massacring populations with just bamboo spears; and Shogun Total War's militastic simulation has done little to allay that. Having discarded Shogun's 3D battles, Paradox's Sengoku is focussed instead on being the best simulation of feudal politics in Japan around. This introduces a lot more seriousness to the world, through seppuku, honour and concubinage, as we'll see - but it also forces us to talk about Bungo, Bingo and Hitachi with a straight face.
In Japan after 1467AD, there was a total collapse of the Ashkage shogunate, for roughly 200 years - the warring states period. Each feudal land-holding clan - including those of Bungo, Bingo and Hitachi - became a potential new Shogunate. The aim of Sengoku is to have yourself elected Shogun and for that, your clan needs to survive, so you need to get married, have children and gather Daimyo - feudal warlords - beneath you.
Using elements of the Crusade Kings engine, Sengoku goes into Football Manager levels of depth with each character, ranking your honour, martial ability, diplomacy, intrigue and so on. Each character, from your son to your wife to your worst enemy, is also rife with personality traits, which help determine whether they like each other or not and affect their general behaviour. For example, a clan leader may be beautiful, paranoid, a misguided warrior and content whilst his son will be envious, ambitious and deceitful; such a son will be relentlessly plotting against everyone, including his father, so will need careful management and promotion. (Notably, AI characters work together to plot against each other and you - they will only move as a group against a clan leader if they think there's a good chance they'll win - or at least threaten him enough for him to pay them off. There's even a plot organiser screen, for single and multiplayer).
Alternatively, you could just remove him. The simplest way of doing this, if his honour is low enough and the clan leader's is high enough, is to order him to kill himself - to commit Seppuku. This gives his descendants great honour. Of course, it's quite likely he'll refuse to do so, and the two characters will now hate each other. In case, the master of your guard can hire ninja for you, who can just remove him the old-fashioned way. If all else fails, there was no patrilineal inheritance in Japan at this time, so you can just pick a different family member to be your heir - if your vassals will follow him.
The key resource that ties this game together is honour; honour is what determines who follows your clan. You can gain honour by exchanging hostages, by building temples to your religion, by rewarding honourable vassals, honouring alliances, and so on; you can spend it by doing amoral actions, like attacking someone (especially if you've exchanged hostages) or using assassins. A character with low honour is unlikely to be able to unite Japan, or even his vassals; a character with high honour can lure vassals away from other clan leaders, and won't be subject to rebellions.
If all else fails, you can go to war. War in Sengoku is very different from Shogun; it's a numbers game and is further complicated by the way armies were maintained in Japan at this time. At the start of this era, armies were rare because of the long peace; by the end of it huge armies met in pitched conflict. Each province has a feudal army associated with it, mainly for the suppression of the regular revolts from crazy religious types, but as the years go on more experienced mercenaries will be available and the wars just get bigger and bigger.
Sengoku is looking hugely attractive, especially to fans of Europa Universalis or Hearts of Iron. There's so much design love here: its multiplayer handles up to 32 players in real time; the world itself is extremely attractive; the menu system is nicely streamlined (we especially like the people finder, which we used exclusively to look for more wives); all over, it's a well-designed sim of intrigue and honour in Feudal Japan. With a little bit of Football Manager thrown in.