Tell me: what are the biggest, longest-running RPG series? Final Fantasy? Dragon Warrior? Ah, you're forgetting Koei's Romance of the Three Kingdoms, with 11 proper installments dating back to 1990 and 5 spinoffs. This series has a lower profile than the others, and that's because it's a tad peculiar. You see, every single game in the series is based on one novel, a Chinese historical epic by Luo Guanzhong. This already sets the game apart from almost all others - the only other book-to-game adaptations that I can think of are Parasite Eve and, regrettably, Square no Tom Sawyer. But Romance of the Three Kingdoms reaches farther into the annals of great literature: Luo Guanzhong's novel was written in the 16th century and set in the 3rd. It's also about 1500 pages long. To the Chinese, this novel is a cultural treasure, one of the Four Great Chinese Novels. (Interestingly, the Suikoden series is very loosely based on Outlaws of the Marsh, another of the four.)
So how do you make a 1500-page historical epic into a game? As it turns out, quite easily. You see, the book covers a period of time in Chinese history when China was split into three warring kingdoms, each of whose leaders strove to unite the whole country under his own rule. So, most of the book consists of descriptions of battles and tactics, as well as accounts of military heroism and long lists of officers' names. It's perfectly suited to a strategy game, which is exactly what this game is.
The gameplay is very simple. There's a map of China which contains a number of cities. At the beginning, each city is under control of a certain ruler, as described in the novel. You can choose which ruler you want to control. Then you have to build up your economy, train an army, and fight your neighbours until you conquer all of China. Along the way, you can recruit huge amounts of officers, all characters in the novel. Some are good fighters, others are good diplomats, others are charismatic and loved by your subjects, and so on. That's basically it. The game lets you play six different "scenarios," which are basically episodes from the novel. The only difference between the scenarios is who starts out in control of which cities. The objective is always the same.
There are a few details to keep things interesting. You can make alliances with other rulers as well as war, but of course you have to break them if you want to beat the game. You can bribe barbarian tribes to attack your enemies. You can send spies to sabotage your rivals' cities by burning down barracks or granaries. You have to pay your officers a salary to keep them loyal to you. You can find rare weapons and items to improve your performance in battle. You can buy siege weapons and train your soldiers as infantry, cavalry, or archers. You can also build ships to travel on water. And best of all, when you're fighting, you can have your officers challenge the enemy officers to one-on-one duels. I have no idea if you can influence the outcome of the duels (it seems to depend only on the Power statistic of the combatants), but they have cool music and the fighters trash talk each other using expressions from the book. And by the way, although the music in this game isn't so great overall, one of the battle themes is really awesome.
The game also has a very versatile challenge level. For example, if you play the first scenario as Cao Cao, you'll start with many good officers, and you'll probably have an easy time crushing your enemies. But if you play as Liu Bei, you'll only have one city and two officers, and you'll start right between Cao Cao and Yuan Shao, so it will be very difficult to survive. If you pick one of the more obscure rulers, you'll start in an even worse position. But if the game gets too hard for you, you can also play as more than one ruler simultaneously: just have them surrender to whomever you want to win in the end.
But most of all, I must say, it's just cool to re-enact some of the conflicts from the game. In some sense, this is the game's weak point, because Koei doesn't bother to explain anything about the game's plot. If you've read the book, everything will be instantly recognizable, but if you haven't, you will have no idea what is going on. There's no dialogue as such, so if you're not familiar with Cao Cao, Liu Bei, Guan Yu, and other figures from the book, you won't really know why they're fighting or even how they're different from each other.
But in Koei's defence, it's awfully hard to explain a 1500-page novel in game form, and the game's Japanese audience is more likely to be familiar with the source material than Americans. That's why this series hasn't done so well in the United States. And the gameplay in this particular installment in the series, while detailed, may get monotonous after a while. But if you are familiar with the book, you'll have a lot of fun playing through one or two scenarios.