Are you categorically against reading books of certain styles or elements? Say, for example, you've heard good things about an author or a book, and you click through to read the blurb to see if it keeps your interest.
You're reading along, and it all looks good, until—wham!—there's an element in there that you just loathe.*
What are your absolute non-starters?
*Full disclosure: Mine is anything with a touch of magic, or magic realism. Ugh.