I’ll go with the low-hanging fruit: Mein Kampf. I’ve read it, cover to cover. As a piece of propaganda, it’s good. As an example of good writing? Absolutely not (though I will admit I have only read it in translation). Oh, and the whole fascist, racist, and generally shitty worldview of the author that he infuses into the text. And the fact that the author is literally Hitler. You 5-star that book? You’re a Nazi. Period. And as a Jewish person, I don’t look too kindly on them.
The evidence said another though the good one of those type of books still got review around 4+, hence I think most people vote like me and didn’t have one standard criteria.
Some book if it fullfill their purpose like I have fun while reading and it is a page turner then I would give it a 5 star but if that same book happen to short list booker price then it might 2 or somthing like that.