No extra plots, no new enemies, no new game mechanics (ehh, sort of you do have to earn the respect of a Jark if you want to buy land, but this isn’t exactly new new, y’know?), no new dragons.
Instead, Hearthfire added a The Sims-esque element to the game by allowing players to purchase land, build a home, and raise a family (albeit having children via adoption). In 2012, Skyrim released an expansion pack called Hearthfire, a DLC that fans *thought* was going to be a follow-up to the critically acclaimed Dawnguard DLC.