I grew up with Nobunaga's Ambition for the NES. It's very simplistic- there aren't even any generals, just your daimyo. Combat takes place on a small hexagonal grid and it's really just hexagons fighting other hexagons. The one thing that really stands out in my memories is the little animation you'd get if you successfully sic'ed a ninja on a rival and assassinated him. *ka-chop*
Nobunaga's Ambition: Rise To Power, for PS2: This one has good music and character portraits... and horrendously broken AI. Seriously, it's bad. Battles take place in real time. There are no waypoints- you can only click where you want your units to go. This means that the AI opponent takes the shortest route to the goal, while your units stumble into trees or walk counterclockwise when you want them to walk clockwise. There is no fog of war either, so the AI always knows what's what and instantly reacts to any trigger. I usually exploit it by sending my units all left or all right, with the occasional decoy.
The game uses the basic infantry/cavalry/musketry setup, except the cavalry are a little unbalanced. When they use skills, their speed and power increase so much that it's like they tied rocket engines to their horses. -_- Oh, there are cannons too - tremendously slow and weak, but it's very gratifying to siege buildings and watch the enemy run for cover.
One of the thing the game does well is let you build up your fiefs and play with the buildings. It's a sort of Sim Fief with pillaging and looting. All buildings except the keep are destructible in battle, so if I'm in a bad mood, I destroy everything. Usually I just prune the buildings I don't like.
Couple other notable points:
- Warrior maidens! Sometimes your daimyo gives birth to a daughter that can either be married off or become a general in her own right. I spent lots of time resetting for maidens- I guess I was setting up a genderbent history of my own.
- Betrayal! Recruiting an enemy general is really hard, but when it works, you can have them switch sides mid-battle. Yoshitatsu Saito is a good pick in the early game, and that scoundrel Hisahide Matsunaga can always be counted on to switch sides.
- Slaying your enemies! Sometimes generals are killed in battle, and if you catch them, you can choose to kill them, recruit them, or release them. You can tell if a general is lousy if they beg for mercy.
Nobunaga's Ambition: Iron Triangle: This one is basically all-RTS. I didn't get very far in it, only played the scenarios with small groups of fiefs. I believe there's no cap on troop numbers, so if the enemy outgrows you, it's hopeless. Your food supplies start draining away the moment any combat is initiated, so I never had enough food for battles.
There's one thing this game does better than its predecessor- you charge up a morale bar to use skills by fighting, whereas in the previous game, fighting drains your morale so you have to rest often.
The game's way of handling skills is odd- there are tech trees, but it requires tremendous investment to research skills, so you usually focus on one kind of skill (infantry, cavalry, muskets, naval, civil engineer, keeps) or get stuck.
Pokemon Conquest, for DS: Koei is listed in the credits, so it counts. This game is basically simplfied Nobunaga's Ambition with simplified Pokemon. It shouldn't work, but it does. Can get repetitive at times. The main campaign is actually a giant tutorial where you can play at your own pace. There are 40 or so post-game missions, though most of them are mirror images of each other with different starting generals. You play as a non-canon character in the main game, and as the various generals in the post-game missions. I got bogged down in Hanbei's campaign... he's so boring -.-
I could go on for hours, but that's a quick list. I don't play imports, and I have no idea how many other Nobunaga's Ambition games have been released (skipped the SNES ones).