The game itself is awful and that detracts from the experience. Then there's the fact the voice-acting is mostly terrible. I can't very well cover my ears from teh dreadful acting while trying to listen to the awesome tunes.

I did take a listen to XSII's OST and it is very good. Though I still say amidst all the crap in this game, this song was really nice.
YouTube - Xenosaga II Soundtrack: Labyrinthos

Really if you can stop yourself from stabbing out your eyes after the first disk, Episode II can become mildly good.

Also yes...Episode 3's OST had a lot more variety and is probably better overall. But Episode 1 was still awesome. It's Mitsuda so what can you expect.
YouTube - Xenosaga~Pain