[I own the new one for PS2 (and by new I mean like a year old), but I still haven't actually played it. I've mostly just read the manual.
The newer one is pure top-down strategy while the one I think you're mentioning is Part X, a hybrid of strategy and many RPG-lite elements.
I'm a HUGE fan of Nobunga's Ambition for the original NES.
Nice, I liked Nobunaga's Ambition as well. There was a sequel for it for SNES called "Lord of Darkness." They omitted the title "Nobunaga's Ambition II" for the U.S. market, presumably to name it something more glamorous (?), but an inadvertent effect of that was that many fans of the original NA had no idea it was the direct sequel. IIRC, Nobunaga's Ambition had only rulers and no subordinate officers, but Lord of Darkness brought in a very dense cast of subordinates. I liked it the most in that series (of the lone two).
Are you familiar with the Kessen series? Kessen I and III are more cinematic albeit slightly less strategic renditions of events in Nobunaga's Ambition. Kessen II is the same idea but set in the Three Kingdoms period.
-BPK