A Falcom game through and through (AKA, must play)
While Nayuta is definitely less crazier than other entries of Kiseki series, it doesn't mean the game's storyline is predictable - in fact, quite a few twists are pulled here and there. Also, it is surprisingly heartwarming, which makes it worth to play until the very end.
The gameplay is excellent - fully utilizing PSP's control, in addition to having balanced difficulty; not overwhelming, but not too easy. The boss battles require the player to figure out their weaknesses, which can change a few times even within the same battle.
The quests may be overwhelming for those unfamiliar with Japanese, so I suggest having a dictionary in hand while playing. No worries, however; NPCs and the stages required for the quests are always marked, which makes things easier.
As for the tracks? Excellent. Admittedly, I didn't like them much at first, but after playing the game, I feel they suit the game perfectly, and love them so much now.
In short? Buy, buy it. No need to worry about other entries in the series; this game, despite having Kiseki tag, is a standalone.