I've been playing since RB, but mine's very recent, BW2 actually:
Let me start off by saying that I believe that BW(and its sequel) is an incredible game. The characters, the music, the starters, the cover legends, the Pokemon, everything in it, I loved.
(I really think that Gamefreak are in a very tough position right now, can they really top BW?!)
In BW2, after the main game, and after all the sidequests and routes, I made my way to the very last area: Nuvema town, the beginning of BW.
Bianca showed up (I love her) and told my new character about her first adventure with my old character. She told him how they held hands and took their very first steps in their grand (and maybe naive) adventure. She then battled me and the BW Rival Theme played. I swear you have no idea how happy that song makes me!
After that difficult battle was over (I was doing a mono-grass run and she took me by complete surprise!), I walked into Nuvema, and its theme started playing. I barely even remember the theme, but when I walked into that town, it sounded like something I've always known
It all just hit me. I was sitting there, in real life, with all my friends around me, they were playing other video games, having dinner, joking around, whatever, and I was just sitting there fully immersed, on the verge of tears and I don't even know why.
I know I wasn't gonna put the game down, finishing the story and visiting all the areas means I can finally start breeding and EV training. But when I reached Nuvema it felt like something has ended and I really did not want to let go.
The only game other than this one that made me feel like I really didn't want to finish it was Wind Waker. (When I realised I was actually minutes away from the final boss I paused and I was considering stopping and leaving the dungeon!). But WW didn't put me on the verge of tears. This sounds very dramatic and silly now that I'm saying (typing?) it out loud, but I don't know.
It was something.