I was not so interested in hearing Xenosaga at first, but out of a remaining respect for Yasunori Mitsuda from his Chrono Trigger days and a hope that such a big-name title might somewhat live up to expectations, I gave it a try. Not only does the soundtrack live up to expectations, it in some ways raises the bar for RPG soundtracks to come.
Xenosaga is not unlike other RPG OSTs in mixing live orchestral tracks with synth tracks. What separates it from others is its success in merging the two into a cohesive whole. According to Mitsuda's Procyon Studio website, only a few of the tracks on Xenosaga OST are synthesized by the Playstation 2's sound chip. The rest were sequenced and recorded by Mitsuda on studio equipment. Though obviously there's still a difference in sound quality between the orchestral and synth tracks, it's not so pronounced as to cause jolts in the listening experience; the soundtrack moves very smoothly between the two.
Xenosaga the game appears to lean very heavily towards the sci-fi direction, and the score certainly echoes that. Mitsuda tries so hard with the B-movie-sounding synth/orchestra "Opening" to make clear the sci-fi course of the soundtrack that the track almost suffers from being cliche. Fortunately a few slight melodic flourishes thrown in at just the right moments make the track a worthwhile listen instead. A great number of the remaining tracks hold true to the sci-fi feel.
The score is likely the most successful attempt I've heard yet at adding cinematic mood to the RPG experience. "Suspense" is subtle yet surprisingly effective at establishing its namesake atmoshere. "U-TIC Council" and "Albedo" forgo some of the subtlety but are still every bit as rife with mood, while not alienating the listener with excessive ambiance.
The most striking tracks tend to be the ones given full orchestral performances, beginning with the wonderfully moody, mysterious opening in "Prologue". "Gnosis" radiates a sense of epic adventure, but in a much more evolved way than your standard RPG score. Its powerful brass and exotic tinge give it a feel akin to "Stargate" or "The Fifth Element". "Omega" may be the best of them all though - an extremely effective tension-building piece that supplements the strong orchestral presence with solo trumpet, electric guitar, and Gladiator-style classical guitar all at precisely the right intervals.
Several tracks also feature a chorus, which Mitsuda wisely utilizes to add mood rather than striving for pure bombast. The almost ghastly male vocals in "U-TIC Council" make it rife with lurking menace, while the beautiful chanting in "Resurrection" indeed almost gives it a spiritual quality.
The requisite battle tracks are of course present in the likes of "Battle", "Fighting Kos-Mos" and "Last Battle", and though they might not have the rock-out quality of other RPG battle music, they're well-orchestrated, dramatic, and fit in well with the rest of the score by incorporating themes heard elsewhere. The chilled-out, progressive ambient "U.M.N. Mode" offers a nice respite from the serious overall mood of the score, sounding like the environment music for some uber-cool space station. And the often-referenced theme for Shion is quite touching, especially in its piano renditions.
The Shion theme also serves as the base for the soundtrack's theme song "Kokoro". It and the other song, "Pain", are fine if you can deal with over-enunciation by the vocalist and the occasional emergence of a Celtic-style flute, which really has no place in this sci-fi score. But the songs definitely take a back seat to the instrumentals.
Xenosaga Original Soundtrack is the first RPG score I've heard that succeeds in creating cinematic drama through its entirety. The trade-off is that some of the elements considered staples of the genre have been diminished; the hummable environment themes, the rocking battle themes, the emotive characters themes are present but not as prominent as in classic RPGs. I don't find myself coming to the soundtrack specifically for certain selections as I do for Mitsuda's Chrono Trigger, but every time I do give the album a listen I come away impressed. As an even mixture of RPG with cinema set in sci-fi trappings, it's a successful step into new territory.