This prompt is really unfair for a bibliophile. Seriously, books? Love 'em. Almost all of them, anyway. I read, on average, 125 books per year, so there are a lot of books I love.
There's Robert McCammon's Swan Song, which I've so many times that I wore the binding out. I used cloth athletic tape to hold the book together until the pages started falling out. It was out of print for several years, so I couldn't even replace it. Finally, Amazon turned up a copy. Now you can find copies anywhere, but I really hate the new cover.
In the same vein, I really love Stephen King's The Stand (unabridged version). There have been accusations of one author ripping off the other, since they're both post-apocalyptic novels with good and evil battling it out. I don't see it. Yes, there are similarities, but that's pretty much the formula of the genre.
As for a book I don't love, there is one, written by a distant family member. It's a truly awful book, with poor writing, lousy editing, and even worse formatting. Under Amazon's new self-publishing rules, her book would have been pulled due to errors. If it wasn't for vanity publishing, this book would have never made it to market. I'm not knocking self-publishing, which in my mind is a totally different critter. I'm specifically talking about those publishing houses that you PAY to publish your books. I'm certain this particular distant family member probably paid at least $5,000 to get her book published.