I am currently playing Fall of the Samurai and having a jolly good old time blasting Japan to pieces. However, the super effective artillery (possibly heath seeking at higher levels of experience) and the Mexican stand offs that are line battles with volley fire (devastating after 20 seconds) are starting to grate on me. I miss masses of infantry fighting it out while being occasionally menaced by arrows.
Therefore my evil plan goes as follows: Buy the Rise of the Samurai DLC without buying the original Shogun 2 base game = 30 euros saved. I have not been able to find anyone saying this won't work considering FotS includes the entire base game's engine and has space on the main menu for RotS.