Ranni's questline is great, but so far that's about the only one I think I've finished. There are a bunch of other ones that are interesting, but I'm not sure where they're going/if there's more to them?
Some spoilers here:
- D, hunter of the dead, Rogier, and Fia: So, Rogier wanted to find the truth of the black knife assassination and I talked to Fia about it. Went and got the proof that it was Ranni's doing, and then around then Rogier died. Later D helped me kill a black knife assassin, but then not long after that Fia wanted to find the owner of a dagger, and then she apparently kills D and turns out she was a 'those living in death' member and she vanished? Haven't seen her since.
- I met D's 'twin' in the underground and gave him D's armor set, but nothing has happened after as of yet
- Gideon's daughter... uhhh... I forget her name? I met her in Stormveil, she helped me kill Godrick. I later met her at Roundtable and then again briefly at the Village of the Albinaurics, but I haven't senen her since then.
- There's the blind woman who wants to be a finger maiden, I fed her a few grapes and then later the burned grape, and she reaffirmed that she wants to be a finger maiden, but again I haven't seen her in a while
- This is probably the other most interesting quest after Ranni: Millicent. I saved her with the needle in Caelid, then later gave her the prosthetic arm and she just told me she'll join me in battle sometime. So I'm assuming that she'll join in a boss fight later in the game
(if it helps for timing, I just entered the capital city proper in terms of game progression)