A similar experience to the above.
Juniper Time by Kate Wilhelm; the previous book of hers that I read "where late the sweet birds sang" was stunning, what other writers would have made into a 3000 page trilogy she delivered convincingly in one book, with each section interesting, readable and ending well.
In contrast, "Juniper Time" is heavy going, you don't really get where you're going with the story for most of it, the characters aren't likable, it's got lots of "filler", magic injuns, unpleasantness that isn't essential to the story (in fact lots of stuff that isn't important to the story) and I DNFed with about 20 pages to go (of 280) - life is too short. I skimmed the ending, it's not only "not good", it makes me feal worse about suffering through the rest of the book.