I don't know if these fit your current playstyle since they're more specific to certain types of characters, but these were some of my favorites that I can remember at the moment:
I always made separate characters for each playstyle/faction I wanted to join, so when I made my archer, the Hunting in Skyrim mod really helped make it more fun and immersive, since the vanilla game has no specific faction for this kind of character. Basically this adds new quests, animals, craftables, NPCS, locations, skill trees, etc. to make being a hunter/ranger an actual viable build in the game.
And because I loved the Dark Brotherhood, I was really sad when the main quest ended and the final repeating quest was so lackluster, so I got The Dark Brotherhood Resurrection and the Dawnstar Sanctuary jumped to life, with new NPCs (DB initiates that actually have personalities!) and questlines. It's a shame otherwise, that you have this cool new sanctuary and you can't really do much with it.