About 25 odd years ago, Michael Moorcock, any books, either in French or a bit later on, in English. Gave up after a few pages, bored to death. Peter Hamilton's the Dreaming Void, after a hundred or so pages, when there was some kind of episode of "Location, Location, Location"* with someone buying a place in some unremarkable planet. Yawn! Give me a 200 pages Jack Vance full of weird wonders any time!
Also, I couldn't get into Hyperion, or A song for Arbonne, eventhough I'm a fan of Tolkien. Also, a load of French Science Fiction. They are a few remarkable ones, but as some acquaintance said 'Good ideas, but some authors write with their feet.'
* British property search program.