Dear Jesus that game is not worth suffering through just for the OST. I have a certain hatred for it's art style, specifically toward it's female characters looking like goddamn moe aliens (I am very picky about my moe), and I found the combat to be lackluster. I am talking about the first Xenosaga, and I have not bothered to play any of the other ones. But I got 10 hours in and the amazing OST was all that was doing it for me.
You're not being harsh enough. For a Mitsuda game, that OST was mediocre. And the artstyle is HORRIBLE. AND, lackluster doesn't even begin to describe how awful and repetitive the combat in the first two games, especially 2.
3, however fixes everything and more. I've never seen a game learn from its mistakes this much and make such a huge turnaround. I'm one of the biggest Xenosaga 1 haters you'll meet, but god damn 3 is good. 2 makes some improvements in a couple places, but overall its just as bad as 1 is.
Xenosaga 1 and 2 are bad games. Xenosaga 3, however has been nothing short of amazing so far.