"Tales of Symphonia". My favorite game of all time. the story was great, the characters were great, the combat was great, the art style was...well you get it by now. Loved that game.
And in a VERY close second place (seriously, Tales of Symphonia only beat it due to nostalgia factor), is "The World Ends With You". That game was !@#$ing amazing. Deep, well layered story that's a blast to go through multiple times, really interesting characters, and a combat system so insane and fun that you actively WANT to get into fights for no other reason than because they are so fun. Everything about that game was top notch, and totally awesome. If you have a DS and have not played that game, DO SO PLEASE.