It's a nice way to experience old MapleStory's world and general charm in a format that very much respects your time. Movement feels a lot more fun, level designs are generally more thoughtful and there's just a whole lot less filler. The plot keeps you moving through the world and the gameplay requires much less grinding.
The story was also more interesting than in anything I've seen from main MapleStory.

...but that's not to say it's perfect.
In exchange for its much faster pace, MapleStory DS trades away the exploration and open freedom of the original, and the options you have to explore the world.
The main story is generally set in a very linear path, and backtracking, even after the game is complete, is fairly nonexistent.
The game world itself also feels very small, partially because of the shrunken maps, and furthermore disjointed as a result of the plot involving portal malfunctions.
The soundtrack is also... very low quality.

But it's worth a play, even if only for a single run. I enjoyed the Thief playthrough, and liked it more than what I've experienced of the Warrior route; I would at least recommend the former - if you can read Korean, anyway.