>>41985910I think the main reason is that there's just so much stuff to do. There are two regions to explore, and it actually feels like it this time thanks to most of Kanto's dungeons being restored. The post-game is also pretty extensive, with there being plenty to do with the high leveled Pokemon you trained up. Even once you beat Red, you've still got the Battle Frontier to work through.
It also combines the design philosophy of the first couple generations with the QoL enhancements of Gen 4, which I think gives it a pretty unique appeal that pretty much only exists in HGSS. The only shitty thing is that it didn't fix the two biggest issues with GSC, those being the level curve in the middle of Johto and the lack of availability of Dark types until the post-game.
>>41987639That's not entirely true. The Kanto Gym Leaders had their teams adjusted to be a suitable challenge for a team that had just beaten Lance. The only real problem is that stretch starting when you leave Ecruteak and ending around when you get to Blackthorn.