For whatever reason, Hoenn seems to be the one region I keep coming back to when it comes to Pokémon. Maybe it's got to do with a general fondness for the GBA. Or maybe there really is something special about these games. I find the set of 'mons on offer here to be particularly charming, and it's true that the third generation of Pokémon games added so much so as to sort of set the norm for Pokémon games going forward. There are a lot more options for connectivity to other games besides just trading and battling (record mixing, secret bases, etc.!), contests and battle facilities make for nice additions for those interested, and there hangs a certain sense of mysticism over the game, at least for me... Things like the Regi trio, Mirage Island, and the absurd complexity of Pokéblocks leave the impression that there are secrets waiting to be discovered, more so than any other Pokémon game I've played. And I've also gotta mention somewhere that it's got some of the series' most memorable melodies. The aesthetics are superb (once again, my fondness for the GBA).
That being said, Pokémon Ruby, Sapphire, and Emerald still hold the same flaws as most Pokémon games as well. They're slow-paced, and the structure of the gym challenge can grow stale with the lack of a compelling narrative to push the player forward. There's a reason I retired the game twice during my playthrough—Pokémon games tend to be long and slow (might even say dull!). Gen III stands out to me as one I have a soft spot for, though I recognize that the inherent core of it is not dissimilar from any other generation.