i assume suikoden II systems are similar to V? in wich case meh suikoden 4 is better.
All of the mainline Suikoden systems are more or less built off of the first where you had your MC plus 5 in two rows of three either attacking, using Runes or Items, or Comboing with other party members. Your Out-of-Battle concerns was mostly sharpening your weapons, attaching certain Rune Pieces to your weapons, or Equipping a piece of Headgear, Armor or Accessory/Item (the last of which gave you two slots to work with).
Two gave you three Rune slots to work with along with hidden skills and a elemental proficiency mechanic that affected damage (and/or failure rate in Viki's case), and a Support Character slot (for plot purposes). You also got a third Accessory/Item slot to work with in your OoB setup.
Three was the most radical change since now you had to actually run up to enemies to whack them in the face and needed charge times for spells, on top of requiring your battle party to pair into three groups of 2 (or in certain cases, namely Hugo and Fubar, one unit mounted on top of another), along with Skills for Combat and Support Units in addition to making Magic Proficiency visible for added OoB customization.
Four cut your active party size down to only MC + 3 all in one line (except when on the boat where you could switch between 2 other teams of 4 for a grand total of 12 active members in your battle party; unfortunately, outside of one particular boss fight, this mechanic was almost entirely superfluous/useless since the two non active parties gained nothing anyways and the encounters were still just random trash). I can't recall any other major changes though.
Tactics isn't exactly a mainline game (even if its basically Four part 2), but the obvious difference here is that its an SRPG (you also don't get to recruit 108 characters since your party is focused entirely on combat roles; and in terms of SRPG differences, this one utilized elemental affinities + field effects to grant massive buffs/debuffs to anyone standing on affected tiles).
And Five basically went back to Suki 1 & 2's MC + 5 in two rows of 3 but retained visible skills and added load times everywhere.