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For something entirely new and also massive, can’t beat Prism. If you want something closer to vanilla, Polished Crystal is a great enhancement hack akin to Drayano’s stuff. Alternatively, there’s Fool’s Gold, which is mostly vanilla Crystal, but every Pokémon is completely different (plus Sevii Islands postgame, along with 3rd gen mons, and 4th and 8th gen evos as of the recent update).
There’s also Crystal Clear if you want open world gen 2, but its quality is debatable.