Suikoden 3 was awesome, one of my favorite RPGs ever. Some things didn't work so well, as they tried to transition to 3D, but other aspects worked beautifully. It was a bit different from the rest of the series, sure, but that in no way means it was a worse game. In fact, I have it only a bit behind S2 as my favorite Suikoden, which is saying a lot.
The only real criticism I have is that, even though the focus is split between four characters, the game was still pushing you toward the lamest one, the typical shounen boy hero. That kind of annoyed me, as he was the only one I didn't care much about, but that probably has more to do with my personal tastes. Chris, the female knight, is one of my ALL TIME favorite RPG heroes, as she had a ton of personal conflicts to sort through, and Geddoe, the quiet mercenary, is really cool and interesting. Thomas, who becomes the one who builds up the castle hub, is also fun and engaging to play.
Be warned, though, that this is the embodiment of a story-driven game. There is a lot going on, with the way it's all woven together from separate points-of-view, betrayals, and legends. It's not for someone who just want to hop in and slay monsters.
Finally, the villains in this were wonderful. I don't even know what else to say about them. There aren't many game villains that I've shed real tears over.
