The World Ends With You is nothing short of a pinnacle of its genre.
The story in The World Ends With You is by far its strongest feature, as it carefully straddles the line between extremely compelling and outright confusing without ever falling too far on the latter side of the fence. I won't go too much into detail about the story because just about anything would be a spoiler - the game is designed to provide the best experience the little one knows about what to expect out of the story. A large part of the absolute joy of the game is unraveling the numerous mysteries within it that all come together to form a cohesive, satisfying whole by the end of the game. The characters in the story are also well done and add to the story as well, being interesting, yet not over the top, and memorable, yet not cliche either.
The story isn't the only stroke of brilliance in the game, however - the list of things that aren't strokes of brilliance would undoubtedly be a shorter list. The gameplay as well is extremely unique, and once mastered, works quite well to provide an engaging experience. The battle system is almost always in two parts - your main character on the bottom screen and his partner at the top. Your main character fights using psychic abilities endowed upon him through pins, which are controlled entirely with the stylus, whereas your partner fights using a combo system controlled with the arrow buttons or ABXY buttons. Each enemy you fight appears on both screens and share a life bar, and your characters essentially pummel on them in unison - but you share a life bar as well, so you can't get too complacent. If you control your partner well enough, you can also unlock fusion attacks where you and your partner combine their attacks for massive damage to the enemies as well as a good amount of HP recovery - often crucial to victory in longer battles.
The game offers four difficulty levels in total, with the interesting fact that any other than "normal" must be unlocked throughout the course of the game. The difficulty can be changed at any time and takes effect immediately - and can even be toned down upon retrying a lost battle, which is a very neat feature, as it can save a player from a lot of frustration if he or she enters a battle underleveled for the current difficulty level. Toning the difficulty level down makes battles easier, but it also makes enemies give much fewer goodies, so there's ample incentive to keep it high, too.
The game isn't only battles, though, and the game features the standard traversable environment, where players walk the streets of the city in which the game is set looking for their next goal. A welcome component of the game is that there are no random battles entered just from walking around, so if you don't feel like fighting any battles, you can feel free not to do so for as long as you like (although never fighting any battles will inevitably make boss battles very difficult). There's a good deal of interaction on the overworld, from interacting with other characters to solving some mild puzzles, which all comes together to keep the game fresh and interesting.
There are tons of stores littered throughout town, and an interesting feature in the game is that, as you buy things from them, you become better friends with the person in charge of the store. The better your friendship, the more you can learn about equipment's special abilities, and the more items you can buy from the store, as well.
There are a number of other facets of gameplay that could be mentioned here as well - the game is surprisingly detailed, although the detail can be ignored without too much penalty if you wish - but it's much easier to just give it my blanket approval. The game explains its ins and outs very well as the game progresses and more options are available to the player.
The soundtrack is of particular note, as well, as its composer took some very obvious risks and bold choices in piecing it together. It's a peculiar mishmash of trance, hip-hop, and rock, which sounds very strange on paper, but which comes together to form a downright brilliant and engaging musical score. The game also has a fair bit of voice acting, and while it's nothing to scream about, it gets the job done well enough, and there are a number of lines said during battle that are particularly memorable.
All in all, The World Ends With You is an extremely understated gem that deserves much more recognition than it's received thus far. It's easily the best game from 2008 that I played, and I cannot stress enough how highly I recommend it to anyone looking for an impeccably designed RPG for the DS. It's simply marvelous.