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They're improvements over RS in every way, but are lacking in Emerald's tougher enemy trainers and postgame. Despite that, there's a lot of new content and features, either being a carryover from XY and the past gens' overall improvements, or adding new content and refining some of the more niche features RS had.
Secret Bases went from being something that was just mentioned and then ignored for most players to being fully fleshed out, and with it made the games really feel like a community, due to PSS, Buzznav, and everyone's bases being transferred to you.