I've only played Suikoden III in the whole collection and was very impressed. When Suikoden IV arrived I was let down.
Unfortunately, I was a little too one over. For when I saw Suikoden IV had came out I snatched off the shelf without a second thought, because in the back of my mind I had the impression that Suikoden IV would continue to follow in Suikoden III's footsteps of success. I was dead wrong.
Suikoden IV as an RPG was one of the most bland RPGs I have ever played. It was not the worst I had ever played, but it certainly made me yawn a lot. The story was reletively easy to follow, I remember, a soldier was cursed and left to die at sea only to survive and eventually help the nation who took him in. It might sound catchy to some people, but it was poorly thought out. There were no surprises in the whole story, no thrilling twists or perspective changes or anything even closely following the "page turning" feel of the third Suikoden game. The collecting of the 108 characters was also toned down for several reasons, the number one reason being that you were forced to find nearly all of them in order to finish the game. The story would stop in little segments to which afterward your "leader" would tell you in some form or fashion "Get more characters for us to contiue our journey." and you would basically play fetch throughout the game for characters you would ether not want or feel like hunting down. Unlike in Suikoden III most of the characters looked or acted the same with next to no motivation to join you on your ship.
Speaking of the ship, it was slow and frustating to travel. You had to sail everywhere to get to town on small little island and sometime a person could spend roughly anywhere from ten to twenty minutes getting from one island to the next. A character can be recruited later that can teleport you to places you've already been, but even then, you have to find it by boat first. I've spent more time fighting on the same boat background then anywhere else. Not to mention there are only about ten enemy models in the whole game, color differently at times.
I could go on, but if you are not convinced by now that this is not an instant classic then I highly recommend at least renting this game before you buy it. In a way Suikoden IV taught me a lesson, always do some kind of research before buying a game. Oh well, I heard Suikoden I and II were pretty good, maybe I'll check those out.