Suikoden is a fantasy RPG series -- there are a few sci-fi hints but I wouldn't call it steampunk like FFVI.
The stories always focus on character drama -- each character in your party has a separate motivation, and the plot pulls people out of your party and throws them into it on a regular basis. In many of the Suikoden games, you will end up at odds with people who start out as your friends, and vice versa. This is magnified by the scale of the game -- every Suikoden game has 108 characters who join you at some point. I know this sounds impossible and weird (why choose an arbitrary number of characters to stuff into every game?) but in actual practice every game has about 70 characters who fight alongside you, the rest of them have other ways that they help you once they join you. Of those 70, the plot focuses on about 20-30 of them and gets heavily into their histories. So, the amount of time the game spends on developing each character's personality is probably more than any other RPG, and similar to a game like FFVI, where a character you haven't thought about in a while will suddenly become the focus of the story.
The combat systems of the Suikoden games are traditional turn based and made to flow pretty quickly, kind of like FFX in pacing -- though they don't have turns dependent on character speed -- instead, fast and skillful characters will get multiple attacks. The combat really isn't innovative, except that you get so many characters, it's fun to figure out what their strengths are. In one game, you get a man rumored to be the greatest swordsman alive about half way through the game, and he's awesome, counter-attacking left and right, critical hitting, dropping two or three people a turn. But you also pick up a kid who lost his parents in a battle over his town, and has some swordfighting talent. If you level the kid way up and give him the right training, he can actually surpass the great swordsman by the end of the game. So a lot of the interest in combat is strategic -- it comes from managing your 70-odd troops, and finding good combinations. Like Chrono Trigger, the game has combination attacks that you discover when you add different people to your party (mostly in the later parts of the game when your party grows bigger than you can bring to bear at once).
At some point later in each game, you start fighting full-scale war battles. These reward you for using a variety of characters early on, because all of the sudden instead of fighting with only 6 characters in traditional RPG combat, you're fighting huge turn-based or real-time strategy battles that use regiments led by scores of your characters.
You also fight one-on-one duels in the games, which are basically cutscenes where you control the action by guessing how your opponent is going to attack based on how they taunt you (it's different every time so you can't just memorize a pattern).
The story in Suikoden is always political and involves the conflicts of nations, but it never gets confusing or too dense. You're always focused on your characters' experience, what they need to do to survive, or what they think is the right thing to do (often they are fighting for survival, which also ties in with parts of FFVI for me, and makes it more interesting than games that jump right to the "save the world" motivation. Each game also gives you some big choices to make, which can affect the plot and even the ending of the game. There's usually some romance though it doesn't usually take center stage. The villians are also usually more human, though there are some total monsters as well. Think conflicts like Princess Mononoke -- people with conflicting viewpoints who are willing to go to different lengths to achieve their goals. Many are ruthless.
I don't want to give away too much from any one game, but I'll describe the beginning of one of the games if anyone wants a better idea... it'll have to wait until tomorrow, though. Right now, I'm going to bed.
