... not really DLC .. but the Mod Support for Skyrim and Fallout 3, F:NV, and Fallout 4.
The games themselves were, eh, meh, arright, but the Mod Support was absolutely phenomenal. That level of Mod Support/ability to Mod the game was the best thing about those games and probably the best thing about ANY game ... ever.
Yes, there's been some phenomenal DLCs in lots of games, but, I don't think we'll ever see anything on the level of the Mod Support those games had for a long time ... at least not until AI-assisted development reaches a level of sophistication where devs are pouring out packets of 10 full-sized DLCs with base game updates/patches all at once, once a month ... because AI can do and do much, and do fast.
... but, yeah, the level of Modding allowed in Skyrim - FO4, despite how good/bad the games themselves were, the Modding all together cumulatively was better than any DLC for any game, ever.
Modders can give you all the things,
all the things you never knew you needed.
If CDPR gave us that level of Modding Support, resources, toolkit, CP2077 could have an active life of 10+ years too.