This usually happens because I read the first part and then have to wait so long for the sequel that I forget how much I enjoyed the first. There’s also always amazing new releases that I often let take my focus away from finishing what I’ve already started.
Crooked Kingdom by Leigh Bardugo
I really enjoyed Six of Crows, but it’s been a while and I don’t know when I’ll have the chance to read Crooked Kingdom or if I’ll remember the characters.
Red Queen Series by Victoria Aveyard
I enjoyed the first book, but the second was pretty disappointing to me. I barely remember what happened in the second and I’m not sure I even want to continue the series.
Truthwitch Series by Susan Dennard
I enjoyed Truthwitch, however I never read the second and I feel as if I need to reread Truthwitch before I pick it up again. I only vaguely remember the characters and plot.
Wayfarer by Alexandra Bracken
I really enjoyed Passenger, but I’ve just never gotten around to reading Wayfarer. This is a series I want to finish eventually though.
An Ember in the Ashes Series by Sabaa Tahir
This is another series where I enjoyed the first book, but found the second to be a little disappointing. I’d like to finish it, but it’s not a priority series.
Illuminae Series by Amie Kaufman and Jay Kristoff
I read Illuminae so long ago that I need to reread it before I can read the sequel. I’m already not much of a rereader so I have no idea if I’ll ever get around to it.
The Queen of the Tearling Series by Erika Johansen
I read Queen of the Tearling so long ago and I own the second book, I just don’t remember the majority of what happened. It is a series I plan on finishing though.
Kiss of Deception Series by Mary E. Pearson
This is another book that I enjoyed but it’s been so long now I don’t know if I’ll ever get around to finishing the series.
The Darkest Minds Series by Alexandra Bracken
I read the first book and I really want to finish it before the movie comes out, it’s just another one that it’s been so long!
Stacks to Read 
I usually just read the book descriptions and some reviews (with spoilers!) to help jog my memory before continuing a book in a series. I’m not much of a rereader either.
LikeLiked by 1 person
This definitely happens to me! I think a lot of the time, I read a first book and if I wasn’t super into it, I’ll just give up, whereas if there were a sequel immediately available, I would probably keep reading. This has reminded me though that I need to get hold of the sequel to Jacqueline Carey’s Santa Olivia, which I did read last year and really enjoy. I hope you make some headway with the series’ you’re still interested in!
LikeLiked by 1 person
Ooh, I loved the Six of Crows-duology and Illuminae & Gemina! Although I did miss AIDAN quite a bit in the latter one.. Obsidio is upon us though! I’m looking forward to it so much. Hope you’ll get to pick up the sequels eventually. 🙂
I’m also a slacker when it comes to sequels, to be honest. I even have a Sequel September where I try to focus on sequels as much as possible so I get through them, haha. Two series I’m right in the middle of are the Daughter of Smoke & Bones-trilogy and Miss Peregrine’s. I’m still going to finish the first series, but I don’t know about Miss Peregrine’s. I had a rough time getting through the second book and ended up putting it back on my TBR instead of my currently reading.. Time will tell!
LikeLiked by 1 person
Oh I like the idea of Sequel September! Six of Crows is a duology that I know I’ll eventually finish, but Illuminae is one I think I’m going to have to reread first.
Daughter of Smoke & Bone is one I never finished either. This past year I’ve come to think that if I really can’t get back into a series, there’s probably a reason for it.
LikeLike