I played Kessen once, unfortunately.
What a waste that was.
Kessen 1 was a bit of a blah to say the least. Kessen 2 was amazing, Kessen 3.... not nearly as stellar and quite repetitive.
You want a great Koei RPG with strategy elements. Inindo, awesome game.
Gemfire is a great game.
Rise of the phoenix is awesome.
Nobunaga's ambition rise of darkness for the snes (not the first one but the 2nd release is amazing)
Ghenghis khan clan of the grey wolf for the snes/gen is probably one of the hardest they ever created.
All the incarnations on the ps2 offer a dif spin on the whole experience, they are in no way the same game over and over.
Dynasty tactics 2 is better then the first but are both great.
Never liked PTO although I own them.
Bandit kings of ancient china is one of their first releases, not a bad game but there are better alternatives.
One of the best Turn based war strats I ever played was Shingen the ruler on the nes. Made by Hot B, and it offers a dif take on the game. This time you govern the Takeda clan, and not the usual Oda Nobunaga or Ghenghis khan clans. And on top of it, its completely dif from the Koei offerings.