Pokemon Diamond is my favorite RPG this generation.
Listen, I love me some Pokemon. I just love that tried and true gameplay and those wonderful critters to collect. I've been doing it since 1998 and I was definitely excited to continue the series on the DS. Little did I know that there was an underlying theme to the gameplay that I never delved into before Diamond/Pearl came out. I mean, I've heard about the EV's and the Stab moves and all those things... but I never saw them as essential to my Pokemon quest. Before I would just get the team I wanted, train em up, beat the Elite Four, and that was that (and don't get me wrong, I had a blast doing it).
Of course this all changed once I met my roommate in college (what is it about college and an undying love for Pokemon? I for one love the change in attitude from High School.). He taught me what I needed to know, and then I started making my team. It took a lot of hours and a lot of egg hatching, but after a long while I got my team with the right moves and the right stats. It was definitely an accomplishment to do such a thing... but the bigger accomplishment was when I beat my roommate (handily, I may add). The student had surpassed the master (and he wasn't very happy either 
).
So here's to you Leafeon, Infernape, Tyranitar, Alakazam, Garchomp, and Regice. You guys rock my socks!
And yes, SoulSilver is awesome as well.
EDIT: Fire Emblem: Radiant Dawn is a close, close second. I just felt bad enough not even mentioning it, so I had to give it some love.
