Okay, it's time to defend this soundtrack. I hear a lot of people saying how bad of a musician Naoshi Mizuta is, and how his music is uninspired and blah blah blah. People buy this soundtrack thinking they're going to get highly emotional music similar to what they're used to hearing in the past Final Fantasy games, but what they find is a collection of music whose purpose is only to provide atmosphere. This means that instead of story-driven music, you get music inspired by scenery, and many people are turned off by this and instantly think "this music is bad," mostly because we expect to be taken on an emotional journey with our music, but instead we're taken on a journey through an imaginary land.
Final Fantasy XI is an MMORPG, and unlike the past Final Fantasies, it has a different kind of plot; a plot that has no lead characters, no character or NPC development and just includes the bare essentials needed to get the player on their way in the world. The player takes an active role in molding his or her adventure, just like every MMORPG. It's a very different concept from what someone would normally find in a Final Fantasy game.
In the notes included with the soundtrack for the Rise of the Zilart expansion, Naoshi Mizuta clearly states the goal of his music for this particular game: to convey the ideas of earth, nature, wood, water, etc. He accomplished his goal beautifully. There're a few tracks such as Buccaneers that leave you wondering if Mr. Mizuta recorded those songs deaf, but for the most part each song has an earthly feel to it that fits the MMORPG genre perfectly, not to mention the depth of most of these songs is amazing.
That said, the person who buys this OST shouldn't expect to find many sweeping emotional themes in this score (they're there, but they're done by the other two composers, they're in short supply and you won't find the level of emotion you'd find in other Final Fantasies), simply because it's impossible to have very emotional music accompanying a very unemotional video game. They should expect to find very atmospheric music influenced a great deal by minimalist art music and popular music; music that's repetitious, sometimes is very aggressive, but most of the time is very easy to listen to, and music that is artistic and fits each scene in FFXI wonderfully.
I hope this review can help other people understand this man's style, because he writes truly magnificent music.