I'm over ten hours into the game and I have no problem with the sample quality. While it's not up to the level of the samples used by HAL Laboratory (for example), it's a lot better than Wind Waker, IMO. I think the biggest reason is because the samples are chosen a lot more carefully this time around.
The real-time music changing is likely a reason Nintendo went with sequenced music, as I find this to be very evident in the course of the game. I am impressed with the way the Hyrule Field music blends in and out with the battle music whenever enemies are near. Furthermore, the Hyrule Field music beautifully segues into yet another piece of music when nighttime falls.
Oh, and the compositions are great. I wish they would have included the Faron Woods post-Twilight daytime music on this soundtrack though. That's one of my current favorites.
I haven't played through the game yet (I'm getting it for X-Mas) but I would also like to add in that I HAVE been discovering some bits and pieces of the game's music in the videos from the game on places like YouTube and/or Google Videos. So far, I have yet to be disappointed.
Speaking of the "real-time music changing", I found this attribute in some of the boss battle themes. Take, for example, the boss in the third dungeon--when Link is battling the monster, the music plays a faster version of "Dinosaur Boss Battle" from OoT. When the boss is on the floor and Link close enough to deliver a blow, the music changes, almost as if to heighten the tension of Link finally getting his enemy on the spot. I found this to be a very impressive touch.
Quality-wise, I had no qualms with WINDWAKER's soundtrack as a whole, but TWILIGHT PRINCESS is shaping up to surpass that, both in scope and composition. And while the sound quality samples aren't as good as say, FIRE EMBLEM: PATH OF RADIANCE or any other Nintendo-produced game, they're certainly not any worse than the ones for OCARINA or MAJORA'S MASK.
My full impressions of the music will come as soon as I either a) play the game, or b) get my hands on the official Japanese CD release.