What makes a bad book

I have a couple friends who have had some really harsh reviews lately. I KNOW this is part of the business. I know it is to be expected. We all have to get used to it because it will happen to all of us at one point or another in our careers. What gets me is books are getting bad reviews, or in some situations torn apart, not because it's a bad book per se but for reasons that to me don't make a book bad. In my opinion bad writing makes a bad book. A story that doesn't flow well, if the writer doesn't know the facts on a subject they're writing about, or a book that doesn't make sense makes a bad book. A story that surprised me by throwing in elements of a sub genre I didn't expected? That doesn't necessarily make a bad book. Yeah it may make the book not for me. Not what I expected and I DO believe that a reader has the right to KNOW what kind of book they're getting when they buy it but me, as a reader or reviewer, not liking elements of a different sub genre alone, don't make it a bad book. Is there a way to give that book an honest review, without grading it low but by stressing what made it difficult for you?

I think some times it's hard to draw that line between a bad book and a book that just didn't do it for ME or YOU specifically. Does a book deserve a bad review just because it doesn't work for me? Maybe, maybe not. I think it depends on how the reviewer goes about the review. I do believe that they should be honest. They put their time into reading the book that they should be able to say how they feel about it but if it isn't a BAD book, just not the right one for you, isn't there a way to say that without completely ripping the book apart?

Someone I know had a review done where a conversation about the book by the reviewers was posted. She signed up for this. She knew ahead of time what would happen but her book was ripped apart. Some of the concerns were valid. I completely understand it but others were going on and on about how they don't like books set in this time period so that's why they had a hard time with it. I'll say it again, that doesn't make the book bad. I don't think reviewers should have to read books they aren't interested in. I also think reviews, where situations like the above occur, should get an honest review but one that doesn't purely grade that book on elements that a reviewer may not have been into, but on the book itself. The writing, the characters. Is that even possible? I don't know....