I believe it is a prequel to PSX's Xenogears, which was about a semi-renaissance era world that had ancient robots from the past (future) and a world war threatening to tear apart the world again. Xenosaga takes place in a futuristic world (one that predates even our society but somehow has spaceships) and essentially is the story of a robotic intelligence trying to become human. I never could get into it, but they made three of these and the Xeno series is still strong on the Wii and potentially another addition on Wii U. Hope this helps.
Actually, Xenosaga is a sequel for xenogears, as once you play the third game, you end up fighting the bots from Xenogears. And let me tell you, thats no fun at all unless you are really high level.
I really hope i can win this my Fiances and mine anniversary is coming up and i want to get him something special and he has been dieing for this game for years.