It's one of the best the PSX has to offer. The game is a complete masterpiece and I love the story even if the game as a whole suffers due to Disc 2's production.
By the time you get to Disc 2 which is primarily focused on getting the last of the story out in sacrifice of the gameplay you aren't particularly missing the gameplay because while it is JUST FINE, it's basic and most fights are a cakewalk without a whole lot of strategy behind it. Deathblows are a very cool concept however there's no reason to use the old ones once you get the new ones unless you like the older animations more.
Some fans are working on a rebalance/retranslation patch for Xenogears called the
Perfect Works Patch. This also goes to improve the base game's translation (which while not bad, it was clearly done by one person and some lines read weird) as well and it's about 80% done as of this post. I haven't replayed the game with the patch so I can't say anything about the overall balance of the gameplay but the retranslation is always welcome.
Also find an undub if possible. The English dub is rough even for a 90s era JRPG.