The very, very slow start was definitely something a lot of people pointed out when it was released. It probably takes like, 8 hours or something for it to really get going depending on how much you decide to walk around town and such. Personally I didn't mind it too much, the setting was one of the things that made Suikoden great.
That and people also mentioned the graphics being kinda bland. The cutscene work was great but the classic bird's eye camera they decided to go with didn't make the best of their assets. Suiko 3 feels a lot more colorful.
it was a bit too challenging after a while
The game's actually really easy if you know what you're doing (but I guess that kinda goes for any game).
I made this mistake when I first played the game, but for a long time I just plain didn't upgrade my weapons or buy new stuff and kept going along in the game. At some point I ended up at a boss where it took me like half an hour to beat it because I kept doing like low double digit damage to the thing. I did end up winning, but yeah, if you don't upgrade your stuff the game becomes painfully annoying. Then later the game throws a bunch of gamebreaker characters at you.