I'm not necessarily surprised when people disagree about whether a book is good or not. Sometimes, I understand their objections (or its appeal) without agreeing. And then there are those times when I wonder if they even read the same book I did.
I just finished N.K. Jemisin's The Hundred Thousand Kingdoms, a fantasy novel about a young woman who, after the death of her disinherited mother, is called to the capital to be named one of three heirs to the empire. It was, in my opinion, an engrossing book, novel more in its mythology than in the storyline or voice.
But plenty of reviewers disagreed. One complaint I saw reiterated was that it started off as a fine fantasy novel but then veered off and became, ugh, a romance. This is ridiculous on several levels. First, there is a kiss early on in the book. That should lead an attentive reader to expect more of that later. Second, it wasn't a romance in the girl+guy=happy coupledom. There is some nookie, yes. There is some love, yes - but remember that "love" doesn't just mean romantic love. It means loving your mom, loving your family, loving your God, even loving humankind. Let's just say the love in this book is of the more complicated kind. Third, for goodness sakes, if spec fic readers can handle Heinlein, they ought to be able to handle this. Does sex from the lady's angle have cooties or something?
The other baffling complaint I saw more than once was that this novel was written in a pretentious, confusing style. Based on this, I was expecting something like James Joyce. Instead, what I found was an almost completely straightforward first-person narrative. There is an occasional flashback, which shouldn't confound any reader over the age of 6. The only narrative device that was remotely non-khaki was a series of conversations that occasionally interrupt the main narrative. It's not entirely clear at first who the main character is talking to in these. Kuh-razy, I know, right? Not. Orson Scott Card did essentially the same thing in Ender's Game, and I don't recall anyone saying that book was treading in pretentious literary waters.
I could speculate on why the book drew some of this reaction, but I won't. Your takeaway: Some people are dumb. This is a pretty good book. That is all.