i mean overall the core pokemon experience has never changed, G/R/B, HGSS, Scarlet and Violet. Core gameplay is the exact thing you said, only paid differences are that now a days they do include some expansions (in the oldschool vein) that are often better than the current base games lol. But overall, outside of stuff like pokemongo, the CORE game franchise has largely been unaffected by a lot of the trends of modern gaming. And great choice, HGSS are a highpoint of the series. Might i also suggest Black and White and Black and White 2. the first time IMO they really tried to make the games more story heavy and they succeeded. The music and pixel art in BW is unmatched as well.

If you like the core games I highly recommend PokeMMO. It's the first five games glued together into an MMO and it's free.