Malazan probably. So many people love it, and it looked like something I'd like, I even had a friend also reading it with me. I wanted to like it so much. After one and half books, I realized I couldn't care less about what happened to any of the characters and I didn't understand anything about the magic stuff, so I stopped reading.

Basically, title. On my side, it might be unpopular, but I was quite disappointed with the Mistborn Trilogy. The world is interesting, I like the concepts, but I could just not connect with the characters? I finished the first book and started the second but could not finish it.

Jordan's Wheel of Time. Inside that massive stack of dead trees I think there might be a pretty decent trilogy struggling to get out, but I wasn't willing to read the rest of the stuff in order to find it. Dropped it somewhere around book four or five and never looked back.

I suppose it is the 3rd book in the Seeker series. The 2nd one was already not great, but the 3rd was an incomprehensible piece of trash, a waste of paper and ink. I have never read something so bad, before or after. Goodkind is crystal clear when writing out his rape fantasies, and blabbers incoherently for every other part of the book. I strongly dislike rape and torture themes, so there was nothing of value in the book for me. Years later when I read the Wheel of Time series, I discovered that Goodkind stole all of his ideas from Robert Jordan and then made them significantly worse. What a hack.

The Dark Tower series for me. I enjoyed Stephen King as a teenager, but had never read any of the Dark Tower books until a few year ago when a friend gave me a copy of The Gunslinger. And I really enjoyed it! It's a quick read, I thought it was compelling enough to start working through the rest of the series. I made it through book 2, a little slower of a pace but I made it, book 3 was the same I feel like, maybe it dragged a little more even. By the first few chapters of book 4 , I just wasn't having fun with it any more and put it down.

Ed Greenwood's Elminster series. It gets so much word-of-mouth for being the basis of the Forgotten Realms but it's honestly some of the worst fantasy writing I've ever forced myself through.

Dragon Riders of Pern. I read them as a kid. Tried to reread them as a 50 year old man.

I just couldn't do it. It made me question what my young self was thinking.

Jonathan Strange & Mr. Norrell. It just did not resonate with me in February slightest and didn’t get enjoyable until the final few chapters. I can appreciate it from a literary standpoint. The prose is lovely and the tone is spot on for what she was trying to achieve, but my goodness did I feel annoyed while making my way through it.

Two I have to mention

The first book of Anthony Ryan's Raven's Shadow trilogy, Blood Song, is one of my favorite fantasy books. I just really liked it. The second book was OK, the third was an absolute train wreck. I would have preferred it to be unfinished. Huge disappointment for me.

The Lightbringer series by Brent weeks started off strong. The Black Prism was great in the magic system seemed unique. Second book was OK, good enough I was looking forward just enough to finish the trilogy. Then the third book didn't finish, so I figured he just stretched out the series to milk a few more dollars from the idea. Then the fourth was similar. I couldn't bring myself to care about the next book. Big disappointment.

HONORABLE MENTION: WoT. Made it to book 6 or 7 both times I've tried to read through them. Then the characters, the writing, everything, just starts to piss me off.

Anything by Tad Williams.

I mean I loved (LOVED!) his stories, but my disappointment comes from never being willing to read them again. He paints beautiful worlds, with a rich detailed filled story….But, somewhat ironically, he is the driest author I have ever read. I just can’t do that to myself.

Wise mans fear. Jesus christ what a trainwreck.

Name of the wind has a lot of issues as well, but god damn I was hooked!

I am not even sad that the third book is probably never coming out, the second book killed all my interest.

The Night Angel trilogy. I got about half way into the 3rd book and realized I was just forcing myself to read it. The characters sucks. The MC was either OP or didn't know wtf to do. The authors description of women is mildly sexist. Every girl was some bombshell or ugly as a foot and their only relevance was to be some kind of sex symbol. The book series seems like a neckbeard's paradise

Assassin's Apprentice :( It was a recommendation from one of my managers at work. I loved the other series he recommended (Nightrunner series by Lynn Flewelling, and Kristen Britain's Green Ranger books) so I was super excited to start. I have never read such a depressing book... I think I made it to the beginning of the third book, but I wasn't enjoying them, and I realized they were putting me in a weird mood, so I stopped.

Mine was the Elric Series by Michael Moorcock. It's the only book I've ever returned. I went back and tried to re-read the series years later and they are such a jumbled mess of things happening for no reason just to progress a plot that I couldn't stand them.

Angel Mage by Garth Nix. I thought the concept sounded great, but the book fell flat for me.