People who say skip the fourth game have never played a bad rpg in there life. I say Suikoden 4 plays more like a suikoden game than 3 does. Its not a bad game at all. I actually kinda like it. It is not as good as 2 or 5 though. Two is my fav rpg of all time.
I remember coming off the high of playing 2 and buying three. I was excited but there was something weird about the game. Like the colors or presentation, it was making me feel kinda sick. Then you throw in the battle system where two characters act as one instead of like 2 where you control them individually. I really didn't like that so I decided to take it back. Maybe it gets better but that first impression was just awful. Although I recently decided to buy it again and give it another shot, we'll see how it goes, but my rpg backlog is out of control.
4 on the other hand was an immediate click. Most people complain about slow ship without reading instructions about making it faster, and four man team instead of six when in reality its a 12 man team cause you get a main party plus 2 backup teams. Allowing you to use more characters in the long run. Or was it one back up team? I forget but 8 is bigger than six regardless. Also duels although still rock paper scissors were presented really well in this game which continued in 5. Also war battles which is easily to me the worst part of suikoden games are still bad in this game, but I like how in this game you can just ram a ship board it and fight a normal battle to win.
Now 5 is just wow. Some would say a love letter to the people who played suikoden 1 and 2. This game is great although I kinda don't agree with going with super pulled away camera on static background. With empty black space everywhere. And although you can zoom in. (which keeps resetting) Coming from 4 its just seems kinda weird.
I never played 1 (although i saw someone else do it) or tactics or the handheld game so I don't really have an opinion on them. I'm gonna play 1 eventually though cause it nets you a character in 2 and i just didn't have 1 before i played 2 at the time. but i say go in order of the mainline games.