I absolutely hate it when someone doesn't like my book and writes a negative review on it on a major eBook retail sales site, especially when I don't understand what they disliked about it.
Two of the biggest complaints are that Mark, the lead character in The Nexus of Kellaran books, is "too perfect", and therefore the books are boring. When I communicate with someone who says that, and point out Mark's many faults, they still say he's too perfect. Now I understand. These readers don't like it when the lead character is trying to be the good man, and be the best man he can be. They only like it when the lead character is a bad-ass, and maybe a criminal. These are the ones who hate Superman but love Batman. They love series like the Taltos books by Steven Brust, and hate Lord Of The Rings.
Another complaint I get is that Mark "has it too easy", and they still say that after I point out all of the suffering and horror that he goes through, which may be the most suffering of any character in any book. But I understand now that they hate that he received more than he earned by his own effort, even though he says the same thing in the book. These people would despise a book about anyone who won the lottery. They hate Batman because he inherited wealth, and like Spider Man because his personal life completely sucks, and they identify with his suffering. But when I was a dirt-poor kid some of my favorite memories were of my mom sharing her daydreams about marrying a millionaire (There were no lotteries back then.) and all the wonderful things we'd see and do and have, and I guess that comes through in my writing.
Of course socially conservative people hate the sexuality in my books, though there isn't really that much of it, or more accurately, they hate the easy acceptance of sexuality in the cultures in my books, moreso even than the sexuality of the characters.
The only other kind of complaints I get are that some sub-plot that a reader liked was too short or not detailed enough, even though I write the longest and most detailed books in the business, which is a compliment in a way, but if I acceded to every one of these comments my books would be a million words long.
So, if I want to be able to capture all of the sci-fi and fantasy markets, I'm going to have to write another series about a dirt-poor bad-ass who never gets laid, and not include any sub-plots that don't get completely developed. Until then I'll just try to be more open about the contents of my books in those ways in the books' descriptions, so hopefully people who won't like my books don't buy them, and therefore don't review them.