The World Ends With You is a classic, and should not be missed by any DS gamer.
The story is pretty good, and keeps you hooked through out.
The gameplay is on 2 screens. The top screen is your partner, who you can control by pressing the D-pad in different directions. You can also let the AI control your partner. On the bottom screen is Neku, in which you use pins to attack. They range from shouting in the microphone, to slashing an enemy vertically.
After you successfully land good combos with your partner, you can have a fusion attack, which damages every character (except you) on the screen, resulting in major damage.
Another part is the level slider. You can go to the menu, and slide down your EXP level. When you slide it down, you'll have less HP, but the pin-drop rate will increase, netting you some extra pins.
The graphics are pretty good. Sprite animation is good, background design is great, with big, booming buildings looming down on you, and walls with graffiti on them. The music is also pretty good. You've good some Japanese Pop with English vocals and that stuff. You'll probably want to put them on your iPod if you like the music a lot.
I say that the game is worth getting, no matter if your not a hardcore DS gamer, OR a hardcore gamer.