The Dr. Prunesquallor stuff in Peake's Gormenghast has put me off so badly that again and again I have bogged down when trying to give this book a much-overdue second reading. I've decided that next time I try, I will feel free to skip. Peake obviously found the fluttery doctor amusing, but I don't.
In the opening of Hardy's magnificent Mayor of Casterbridge, there's some line about a bird chirping its trite song. I just about threw the book across the room when I was trying to read this book again and came to that bit. I need to ignore it or figure it's mostly just a reflection of Henchard's state of mind.
I used to not get Bombadil all that much, but I do now, and feel he really needs to be there in LOTR. But I think it is a mercy that Peter Jackson left Bombadil out of his movies. To present Bombadil aright would require genius, and Jackson is a capable craftsman but no genius; he would certainly have flubbed this material. Maybe some other director will give us a new LOTR someday, and, if he or she is a genius, we'll get Bombadil then.
I reread the first part of Blish's Case of Conscience a while ago, rolling along fine, but when the Lithian is brought to a new world, something went way wrong as far as I'm concerned and I didn't finish the book.
In Blackwood's "The Willows," it seems to me the author's confidence in his material sort of collapses when the narrator starts vaporing on about occultic ideas.
In Lovecraft's "Shadow Over Innsmouth," there's a breakdown of artistry (and Lovecraft had been writing well) when he has his narrator questioning the old coot on the dock, and then the oldster sees something and Lovecraft spells out the scream. Actually, in a way it's endearing (I always have to imagine Lovecraft up in his room "sounding out" the letters to get the quality he wanted -- wonder what the aunts thought if they heard him! like something out of P. G. Wodehouse), but I think it more or less stopped me dead on one rereading.
In Malory's Morte d'Arthur, the stuff about the war with Rome is deadly tedious, and my memory is that quite a bit of the Tristram material was tedious, too; I never read these portions now. The rest is mostly wonderful.
In Hodgson's The Night Land, the stuff about the narrator's lady-love is awful. I have tried to finish the book more than once and just haven't brought myself to do it.
I've found, in Studs Terkel's Hard Times, skippable stuff about unions (not all the stuff about unions).
With the novels of Sir Walter Scott, I've found that a safe rule of thumb is to start reading at the second chapter. He is then often really good!