To add some extra replay value to the game, Taito has included some unlockable bonus content in the form of flashier paddles, additional blocks and new music tracks. These can be obtained by first earning coins by completing stages in the single-player modes and then spending them in Arkanoid DS's bonus boutique. Most of these extras have no effect on the actual gameplay, but nonetheless will provide a nice challenge for completists. 

Even at half the cost of the typical DS game, whether or not Arkanoid DS is worth getting is still kind of a toss-up. There are probably several versions of Arkanoid already available on the internet for free. Whether Arkanoid DS is the definitive adaption of the game and whether that status justifies a $20 purchase may depend on how hardcore of an Arkanoid fan you are or what kind of game you're in the mood to play. In any case, Arkanoid DS is a pleasant, addictive distraction. Just don't expect much out of it beyond what you'd see in a free internet Flash game.