Plotting seems to work, that I've noticed. It is pretty difficult woo'ing numerous rival clans into your plot, though, so it's tough to be successful at getting a strong one going.
Most importantly, however, the AI is not shy of using Plots and will utilize them against you and other clans. I gotta commend the guys who did the AI work on this one as it looks to use that unusual mechanic fairly well. I'd like to see what other sneakiness it may be capable of.
To answer the OP:
This game isn't like HOI, EU, and Vic2. While managing your armies and combat will be mostly the same, and some of the same interface features like the map filters are there, the game plays like Crusader Kings Lite. Or perhaps more like an EU Rome VV with more control of the character system by the player. The major features I always find myself concentrating on the most In Sengoku is 1) Getting more income, gold, and honor (currencies); 2) Arranging marriages for good skill bonuses, to ensure the breeders are giving me plenty of courtiers and heirs, getting possible inheritances of rival clan titles, and to get relationship bonuses with other clans through such marriages; 3) Blood and mud, blood and mud (war!); and 4) Plotting, Ninja'ing, and other nefarious means of weakening not only rival clans, but unfaithful vassals and attempting to lure my rival's unfaithful vassals over to join me. This isn't easy at all, but is very satisfying when your intrigues work out.
I think that the game needs more random events, notably character events (with choices) for the player to interact with in a somewhat similar way to Crusader Kings. Right now the player's input into the character system is mostly arranging marriages, bribing, and dishonoring others. More interaction should be added as PI's character system, in their games, is a very strong and unique feature that should be fleshed out as much as feasible. There's definitely more to do in this character system than EU Rome's, so I'm happy with where it's starting from.
The game itself, while having small bugs as most releases do, is quite playable with no huge game breakers. While at first I was a bit hesitant what with the character system being less filled out like CK, I've been enjoying it more and more for all the subtle intrigues it inspires and the overall feel of the gameplay itself. Sure, it needs some tweaking but it's the only thing I've played since I got it, and that says a lot because I'm often playing more than one game on any day.
