TLZ: Spirit Tracks is a great game with a wonderful storyline. Check my review for more details!
From controlling Phantoms in vast and well-designed dungeons to battling various kinds bosses at their end, SP is very entertaining and, as the GameSpot review crew so accurately depicted, it makes your inner child giggle in glee.
The soundtrack is beautiful, and the characters are well-designed and a delight to watch in cut-scenes. I personally prefer the fact that they don't talk with words, just sounds, because it keeps the game light and not all-up-in-your-face.
On the other hand, the game does have a couple of annoying flaws:
First, most of the missions are not very challenging to complete and it's kind of disappointing to finish three-quarters of the game on the first try.
The second and final noteworthy flaw is that it may get frustratingly repetitive at times. From the unavailability of checkpoints to the, sometimes, long and over-designed missions, it is hard to enjoy the game at times if the player has to go through the same drab process several times.
In conclusion, SP is a great game to play on the NDS and is definitely on of its better games. You haven't got the full NDS experience unless you have played any game from The Legend of Zelda series. DON'T MISS IT :)