I've played about 2 dozen turns as Shimazu and it's really lovely. At one point, as I was fighting Shoni and was only a turn away from a third castle to conquer I was backstabbed by a trade partner. They showed with two stacks near my capital and in the chaos I lost all I gained except my starting province. But a few decisive battles later I had the whole of Kyushu (the southern island) to myself. I've seen AI stack it's armies, backstab me when there was an opening, even sneak in an army by sea. What I'm glad I didnt see were the silly one unit speed bumps that were so annoying in the previous games.