World of Warcraft: World Quests
In World of Warcraft's 14-year history, it has introduced and popularized a huge array of designs, but the World Quests introduced to the series in 2016, is still one of the best changes to the WoW Formula, and the MMO genre as a whole.
Prior to World Quests, most of the repeatable end-game content was relegated to dailies. Which meant running 2-3 of the same half dozen or so repeatable quests for a faction or group of NPCs in order to gain reputation, loot and other various rewards. Daily Quests themselves had been introduced during Burning Crusade, WoW's first expansion, back in May of 2007, with the Black Temple content. While in 2007, the concept of Dailies was a huge improvement over grinding for reputation simply by farming mobs or collecting particular types of loot (I'm looking at you Netherwing Crystals), By 2016 running the same