1 is a solid 8 I'd say, but it's fundamentally a different kind of rpg than most others.
I'd call 3 the highlight of the series, but they build on each other.
They're all ugly as shit until you get to 3(not on map or in dungeon, where they've got that timeless suikoden 2 thing going on, but in battle)
which is the first game with a cel-shaded style and the last with Naruke's music, which is a good amount of the reason I consider it the best(though the later composers do imitate it)
To be honest, I haven't beaten any of them completely. One thing to realize though is that they're short games, only 15-20 hours for the first one(without sidequests. With, 30 hours is long.)
Very manageable.
For the first two games, only some characters can use the kickass superguns called ARMs. This leads to a very specialized party system.
From 3 onwards, however, everyone can use arms, with different people using different guns.
If you can get any of them, play it for a bit. You'll figure out fast if you like it or not.
Here's some gameplay of 1.
(Though the dude is mashing through the battles)
https://www.youtube.com/watch?v=P9PSxZQlGj8