I would suggest playing Xenogears before you play this. Xenogears is quite hard to find.

If you just want to play Xenosaga. By all means, go right ahead. I have the game, but after awhile of playing it, I started to dislike it. I hate the main character and her sympathies towards the Realians, and whatnot. Well, that's just my opinion. Get the game if you like. You may enjoy it more than I have.