Z-moves, regional variants and the end of gym battles.
Sun, Moon, Ultra Sun, Ultra Moon · Released 2016
Alola is the Gen 7 region, and the generation that made the biggest structural change to the Pokémon formula since Gen 1: it removed gyms entirely. Instead of 8 gym leaders, Alola uses a 'trial' system where players complete themed challenges on each of the four islands, culminating in a Totem Pokémon boss fight. Gen 7 also introduced regional variants (Alolan Raichu, Alolan Muk, etc. — Pokémon with alternate typings based on their new habitat) and Z-moves (one-use super attacks per battle).
Alola is based on Hawaii — four islands (Melemele, Akala, Ula'ula, Poni) directly corresponding to Oahu, Maui, Hawaii Big Island and Kauai. Hawaiian language is woven throughout (kahuna, mahalo, mauka/makai). Solgaleo and Lunala reference the sun and moon of Hawaiian mythology, and the Ultra Beasts are pulled from a sci-fi subplot about parallel universes.
Sun & Moon shipped at the exact 20-year anniversary of Pokémon Red & Blue, and the in-game Battle Tree features Red and Blue (now adult trainers) as endgame bosses — the first time the original protagonists are explicitly playable opponents in a mainline Pokémon game.