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Emerald was pretty much the definitive version, which incorporated the plots of both Sapphire and Ruby into one which felt far more grand.
Also the Battle Frontier was kind of like that Battle Resort in Shinnoh Region, where after the game was over you traveled to a new place and competed in some seven different bullshit levels of computer cheating battle events where you had to become top rank in all of them. There was some other stuff there, some caves to check out, new items, new stuff to find, it opened up an entire new section and challenge after you beat the game which was decent.
Also there was this guy named Scott who foreshadowed it all along while following you in the game.
By far, Emerald was the best version of this trip, which is why they need to keep a lot of the improved elements there for this version. Though I doubt The plot section will end with both teams summoning their legendary and the world nearly being destroyed because they end up fighting, so you have to get RayRay to make them stop.
To only see one of the legendaries released in this game and the stakes not being as high, it'll feel very half done compared to that shit which was much grander.