24
Gen 2
And yeah, its pure nostalgia. I played Gen 1 when I was 8 I think, and I was just impossibly pumped for Gen 2, and it was everything I hoped it would be. I didn't care that a decent portion of the new pokemon were dumb, plenty of them were awesome, and I could always play with my old bros, too. I didn't care that Kanto was empty, it was more content than was in the first games, and it was hugely nostalgic for me. I loved the mystical, natural feel of the region in contrast to Kanto's more high-tech, scientific industrial atmosphere. I loved the music. I loved getting to buddy up with Lance, who was my favorite trainer in the first games. I loved going back and fighting red.
BW2 and Platinum are pretty outstanding, too, though I didn't care as much for D/P and BW1.
