The important thing is I'm still playing it. I'll be honest. I'm not as avid a gmaer as I used to be. Some games I'll lose interest in them about halfway through, and not play them again. The World Ends With You, I've put it down for a few weeks in the time I've had it, then I come back to it, and I'm tearing through it like I just bought it all over again. Its just that fun.
Its got a very unique fighting system that utilizes both screens at once quite nicely. The bottom screen is for most purposes of this game your main screen and the top screen is where your partner fights. In a battle you can either have them go full auto or control the top screen by way of the D-pad, and at the same time control your main character, Neku, with the stylus on the botom screen. You share a life bar and enemies, so if one monster gets erased on either screen, that's it for them.
The way the attacks are carried out are through the use of pins, that are classified from A-D. You can have a total of six pins for Neku. They all have their own stats, that can be altered through fighting or also through items you equip your characters with and what area of the gae you're in. So one item may make them stronger in one area but in another it may weaken them considerably. I'm aware this stuff isn't new. But the way they implement it offers players a chance to customize their fighting style whether it be melee or long range in a very fun way.
part of the replayability of the game is the amount o customization it offers players. That and the music. You don't get tired of it. It's something like a mix between techno and pop. Its very inline with the feel of the game.