The thing that really creates a difference between STW and the two later titles is the real atmosphere that STW has. Shogun really gives you a feeling of being there on a battlefield in Sengoku era Japan and that's what I think really makes Shogun shine over Medieval or Rome. I can still remember some of my classic battles from my early Total War career in Shogun. One battle that actually made me cry afterwards was a last stand in Echigo with Takeda Shingen and about 500 men facing an Uesugi force of several thousands. My men literally fought down to the last men and I can remember how much I valued their sacrifice. Hell and this took place about 5 am in the morning and I had school that morning, so yes Shogun really was that addictive.