

Are we counting old-school expansions as DLC? If so, then, aside from the infamous Horse Armor, the Elder Scrolls series seriously raised the bar for what to expect from RPG add-ons. Tribunal and Bloodmoon were massive expansions that set the standard early on.
Knights of the Nine might’ve been a bit weaker, but Shivering Isles is one of the GOAT expansions and is arguably better than the base game.
Skyrim kept the momentum going with Dawnguard and Dragonborn, both of which added tons of new content.
The series is straight-up GOATed when it comes to expansions that are actually expansive: new locations packed with quests, items, monsters, spells, etc. They take already huge games and somehow make them even bigger.
Honestly I’ve always hated this. An early example of the awful trend where there has to be a “lore reason” for every little detail.
Star Trek aliens are mostly humanoids because its a human TV show telling stories that have to be relatable to humans and also has a limited budget. There is no need for a lore explanation.
At least in this case it’s a one off that’s never really referenced again.