Ys series. There are...9 total entries, with various re-releases and modernizations. More of an 'action' jrpg, with enemies alive in a world that you can attack real-time. Plus the soundtrack for all games are absolutely glorious.
1+2 is basically the same, with 'bump' combat (move to attack). You either like it or hate it. Depending on the version, boss difficulty can differ greatly (for instance, chronicles has final boss of 1 very difficult, but 2 can be cheesed, but the Ys 1+2 version (from turbografx version) has 1 to be overleveled and die in 3 hits, while 2 is hectic and difficult and your brain feels like it will explode).
3 (wanderer's from Ys) is 2D side scrolling push a button to attack. I grew up playing this so much. Has a remake to a 3D game with a good combat system (Oath of Felghana)
4 has a modern remake for the vita (memories of celceta)(I believe the vita changes the combat system to something not quite as good...?) , for the orginal snes (mask of the sun) back to bump combat, but only using spells based on the specific sword.
5 (lost city of kefin or something) easily forgettable, poor combat system, focusing on alchemy spells and stuff, but a stepping stone to the later releases of games.
6 (ark of napishtim) 3d ps2 game with great combat. Just turn off character voices, as that can ruin the game for obvious reasons.
Origins what I consider the best of the modern combat systems for Ys. Takes place before the events of 1+2
7, never played it yet. Changed the combat system from origins and never got around to it
8, brand new, only in Japan for now. No idea about it.
Other mentions include:
Star Ocean: Till the end of time: ps2 game. One of my favorites, especially once you enter 2nd disc in the story. Makes you feel small, as everything start small then gets larger and larger and out of control, and then completely insignificant. You can control any of the characters, and each have much different playstyles and feel. A pro and con is the crafting system; it is incredibly vast and absolutely required, but has way too many hidden factors and ranges for everything that a strategy guide is needed to do pretty much anything.
Shadow hearts covenant (2): an excellent game with story-telling and characters, environment, comedy, etc. Random-encounter based combat. Only con, is that the fire-spirit can trivialize encounters; charge for major boosted damage, and use a 'key' item for multiple turns in one go (especially with tech ring setting, just don't miss), for something like 250% per turn by 3-9 turns in a single go. Feels like you can one-shot the final boss and many other bosses.
Shadow hearts (1): great game, much darker-themed than the second one (I played the second one first cause reasons). No cheap tactics here, making it much more difficult (or I just sucked at the game).
Xenosaga (1 & 3). 1 was pretty good, but the mechs were kind of mandatory and felt overpowered. Still an enjoyable combat system (turn based, but you hold...charges or combo points or something of the sort for powerful attacks). 3 just enhances everything and makes everything feel better (in my opinion). The second game I feel sucks and should be ignored forever.