I guess Mario Kart DS takes it for its great online functionality and ds link up battles, still hasn't lotst its luster years after its release. As far as just flat game I'd have to say Castlevania Dawn of Sorrow, great quest and best Castlevania since SOTN. Plus you can unlock some sweet playable characters. Alucard anyone.
I think this is becoming more familiar with people, I'm 25 and have 2 daughters and I play pokemon and I have it reserved. I'm a huge RPG fan so naturally I took to pokemon the first time I played it. Fact is this, it is a very addicting RPG. If people call me immature for liking this game so be it, atleast I'm playing quality games. I look forward to playing this, and now that my daughter likes pokemon we have something to talk about at the dinner table.