I didn't played any of the games, what makes this series unique to other JRPGs?
Incredibly strong story, exploring a fuckton of locations for loot, active dungeon puzzles that were genuinely fun and not passive lipservice, fun characters, an overworld theme ripped directly from The Good, The Bad, & The Ugly, extra/bonus fights and some dungeons, earning your super powers, not being bogged down in FMVs as was the growing trend at the time thanks to FFVII....
Essentially it was a good, grounded JRPG in a time where they were about to alter in style and content (again, thanks to FFVII). It took the disc space of the PSX and expanded on a fuckton of content & story progression instead of smothering you in superfluous & vapid filler. There was a LOT of meat on those bones to chew through, and it was a lot of fun finding it all.
Granted, there were honestly a lot of unique JRPGs in the fifth generation, and a lot of new playstyle ideas tried before "Smother them with movies" took over. Wild ARMs was the one where you didn't have to relearn a system, but put enough new content in there where it was fun to master (the ARM tuning and Crest Graph systems).
>Just like what happened to Halo huh?
Halo continued on a story that was essentially complete because m'franchise. Wild ARMs 4th Detonator decided to take their core theme of "hope in the bleakest place of adversity", put it out back, and blew it's fucking brains out.
4 swapped dungeon diving for linear hallways and platform puzzling, introduced a kinda-retarded hop skotch battle system that was pretty damn exploitable, cut back on all the extra content, essentially railroading you all the way through the game with very few deviations. And the story was genuine ass, through & through. "World is hopeless, adults are all dicks, grow up and be a loner away from people" was the eventual message. Sucked so damn bad that it actively turned me away from trying WA5. I couldn't even blame different directors because damn-near all the same staff was working on the title.