Music is an integral part of any gaming atmosphere, and Yuka Tsujiyoko does a fantastic job with it. Most of the tracks are upbeat and playful, however she is able to express other moods according to the environment. A prominent example being "crystal palace crawl"; It emanates mystery with an ominous touch, perfectly describing the level full of mirrors and illusion.
This OST is sure to invoke nostalgia into anyone who played this when they were seven years-old.
*note: I want to clarify that Koji Kondo, although indeed a great composer of many Mario games, DID NOT make the music for Paper Mario. Apparently a few of these ignorant reviewers think that he did.