Its called a story-based RPG for a reason.
Gameplay/Story: Xenosaga puts you in control of Shion, the creator of an anti-gnosis cyborg called KOS-MOS. KOS-MOS was built out of desperation after the human race has been all but wiped out by the mysterious gnosis. It is unknown exactly what these gnosis are as they seem to exist on an alternate plane of existance. The story grows more in-depth with plenty of twists and turns (and even a lot of symbolism into various religions). The majority of the game is run in cutscenes. Literally, these cutscenes can be half an hour to an hour long and when you actually do fight, the system isn't all that interesting. The battle system is your typical turn-based systems with a small bonus that doesn't really feel like a bonus later on. This is the boost system. Every time you attack, your characters boost meter goes up. Once it fills up, you can boost your character which essential is cutting in line so that your person attacks next, despite the turn order. You can fill the meter up 3 times and every time you boost, the number goes down by one. The reason why I say this system doesn't feel like a bonus later on, is because the enemies can do this too. At first, it works well and adds a little more interest in the system. Later, the enemies can and will boost almost every turn. They can also cancel your boosts. This becomes slightly frustrating. Despite, the shortcomings on the actual gameplay, the story makes it all worth it. If you are at all a sci-fi fan, you will love this story and finish the game no matter how much you hate the fighting system.
Graphics: The graphics are weak in the actual gameplay aspects of the game, however the CG cutscenes are absolutely fantastic. The anime-inspired character designs are superb and the environments are very realistic looking.
Sound: The music is very anime-ish but this certainly isn't a bad thing. While you most likely won't be going out and buying the soundtrack, you will enjoy listening to the battle music. I, personally, even started humming along during some of the battles. The downside of this is that it is repetitive and if you don't like the music, your kinda screwed. The voiceovers are ok but far from great. Some characters will appear whiny but overall, you will come to accept it and just love the awesome storyline.
Replay Value: As with most RPG's, there is little value in replaying the game. There are a few sidequests but none with any real purpose. There is one sidequest where you must search out hidden doors and the keys that go to them but this isn't very difficult and you will most likely find them all the first time through. Other than that, there are a few hidden costumes but if you're like me, this isn't really worth playing the whole game again for.
Overall, this game is the essence of what a story-based RPG is. Incredibly strong storyline and incredibly weak gameplay. If you can deal with the poor battle system up until the very end, you will be rewarded with an incredible ending that makes the long haul very worthwhile.