Goal: To have a custom portrait for every unit, agent, and historical character in the campaign.
Methodology: Exporting art from an extremely obscure historical simulation game (Taiko Rissiden V by KOEI) and applying them here. A surgical transplant, so to speak.
Rationale: I enjoy history, and I think Taiko V did a good job in its presentation of characters. Most of the character art there was carried out before KOEI went crazy with over-the-topness in character design, and I feel that the art I will be modding in adds another layer of flavor to Shogun II as a whole.
... Plus, some of the art was, in my opinion, pretty good.

Though I understand purists may not like some of the more modern depictions of historical figures.
4/30: All generals added. Geisha, Monk, Missionary, Metsuke, and Ninja all have custom
portraits.
4/17: Agents updated. Attempted to fix the Hattori faction.

4/12: 
Daimyo pack released - this first mod contain new art for all of the special daimyos found in the campaign.
Preview (EDIT: Gah, forgot Hojo. Shameful display! V He's there now.)

More coming up!
A friendly note: This is my first attempt at modding. I try not to make too many mistakes with packing and things like that, but I think they're bound to happen somewhere. I apologize ahead of time for any glaringly obvious errors and hope you could pardon my noobishness.
I promise I learn quickly!