Quoted By:
1, 2 (and FRLG/HGSS) and 5. Attention was paid to building a world and a story without sacrificing gameplay--Kanto to Johto felt like a natural transition, and playing through both in succession feels like a completed journey after defeating Rocket. Unova to Unova2 is immersive; in the first games, you're effectively playing through a standalone region with it's own quirks and (limited to new) pokemon, while in the second you're both rewarded for exploring familiar territory while not having to dig deep for new content and new stories.
tl;dr most soul comes from the completed story arcs