Final Fantasy XIII Original Soundtrack composer Masashi Hamauzu, whose previous efforts for the series include co-composing Final Fantasy X and fully scoring Dirge of Cerberus, has a reputation for being skilled at composing and arranging for orchestra. Certainly it shows in FFXIII, where his orchestral pieces from a technical standpoint easily surpass those of previous Final Fantasy original soundtracks. When Hamauzu strays from the orchestra, however, the soundtrack suffers, which unfortunately is fairly often.
Among several impressive orchestral pieces the battle theme "Saber's Edge" makes the strongest early impression. Not as adrenaline-pumping as the best battle themes from Uematsu and Sakimoto but more nuanced, its smart arrangement moves from subtle orchestrations and enrapturing piano cascades to a driving climax. The piano is a common element in almost all of the standout orchestral arrangements. In the atmospheric "Lake Bresha" it accompanies rising and falling strings and a motif reminiscent of Soul Blade's "Asian Dawn", in "March of the Dreadnoughts" and "Fang's Theme" it adds spirited accents to boisterous orchestrations, and in "Nautilus" it forms part of a lovely, introspective interlude. Then there's the grand finale "Nascent Requiem", an impressive final battle theme given even greater substance by another fantastically orchestrated, dramatic interlude - a grand finale again much more nuanced and along classical lines than the battle themes of Hamauzu's series colleagues.
Though comprising only a few tracks, Hamauzu's jazzy tracks are also highlights. Both "Sazh's Theme" and "Can't Catch a Break" sound like jazz jam sessions, more notable for the talented interplay between guitar, bass, piano, percussion and horns than any particular themes within. "Pulse de Chocobo" adds an electrified, high-speed jazz intro to the staple series theme, even if the arrangement of the theme itself is a bit predictable.
Once you factor out the dozen or so standout orchestral and jazz pieces, however, the majority of the soundtrack ranges from forgettable to puzzling to downright annoying. Probably the rock and electronica-oriented pieces leave the worst taste, particularly "Snow's Theme", where the generic electric guitars and pompous lead melody sound more like the entry music for a second-tier amateur wrestler than the theme of an RPG protagonist. Only in a few other tracks does an electric guitar surface and then only as backing instrumentation, but in each case it becomes repetitive and grating within the first few bars. The same could be said of some of the electronic tracks. It requires an act of will to get past the first few seconds of "Test of the L'Cie", "Will to Fight", and "Cocoon de Chocobo" simply because the opening loops are so grating. Even among Hamauzu's generally strong suite of orchestral tracks, a few suffer from similar repetitiveness, reinforcing the notion that four hours of music for a single project is probably too much to ask of most composers, even talented ones.
In what seems an attempt to add a contemporary sound to the score, Hamauzu implements airy female vocals with some electronic tweaks in quite a few tracks. These additions range from extraneous at best to obtrusive at worst. Both "The Sunleth Waterscape" and "Cocoon de Chocobo" are almost lost causes to begin with (due to the the trite pop stylings of the former and the annoying synth of the latter), but English lyrics like "Step into the rainbow, find another view, chase the tender light" and "We will have fun, we will have fun" do neither track any favors. In "Sulyya Springs" and the "Will to Fight", as much a problem as the lyrics is the deliberate monotone vocal style, which again just sounds contrived. (In contrast the instrumental version of "Sulyya Springs" in FFXIII Piano Collections is a beautiful, entirely different piece altogether). Then there are the pop songs "Eternal Love" and "Kimi ga Iru Kara", the most irrelevant J-pop drivel to ever find their way into a Final Fantasy game.
The sole standout among the vocal-infused pieces is "The Gapra Whitewood", which thanks to its earthy instrumental tones, less contemporary slant and lovely main theme makes perhaps the most lasting impression of the OST. (The piece is even better in its Final Fantasy XIII Original Soundtrack Plus version, thanks largely to a reduced emphasis on its vocals.)
More than any particular instrumental or vocal stylings, however, my most significant issue with Final Fantasy XIII OST is a more basic and subjective one - its themes simply don't resonate. That's not to say it's thematically void, as certainly there are noticeable themes related to major characters that surface repeatedly, but none make the strong impression of those from previous series titles. "Serah's Theme" seems the main theme of the soundtrack, appearing prominently in no less than eight tracks, but its poppy vocal rendition in "The Sunleth Waterscape" leaves a bitter taste from the outset, and none of the many arrangements that follow manage to add emotional weight to the theme. "Lightning's Theme" starts decently enough, but its cheeky violin chorus sounds like a bad Sonic World Adventure track, while the blatant sentimentality and simplistic arrangements for the various renditions of "Hope's Theme" are akin to what Uematsu would produce on a bad day. The theme introduced in "Prelude to Final Fantasy XIII" holds some sense of wonder and is the most promising of the bunch, but sadly it disappears for most of the soundtrack.
To be fair, the number of forgettable or even slightly annoying tracks in Final Fantasy XIII Original Soundtrack is hardly much greater than other recent original soundtracks from the series. The difference is that most of those preceding Final Fantasy OSTs have certain unforgettable themes and powerful musical moments that make it worth trudging through the filler, whereas the standout moments in FFXIII are neither as memorable nor as powerful. It does have its moments - a decent-sized disc's worth of them - but in general their quality lies more in Hamauzu's skillful arrangement and their high production values than in having the emotional impact most people expect of a Final Fantasy score. With many of those same tracks available on the cheaper, single-disc Final Fantasy XIII OST Plus in mostly similar form, my recommendation for Final Fantasy fans not already familiar with XIII's music but wanting to keep up with the series would be to go for that album, or just download the OST's standout tracks individually. Better yet consider Final Fantasy XIII Piano Collections, which stripped of the many distractions of the OST is a more enjoyable, more emotional musical experience.