There are a a few things I treasure when it comes to reading. Unlike some others, I read for style; for the way the author writes an tries to convey the events in the story. I am in love with metaphors, and so tend to drift towards more dense reading material. I especially love the esoteric. Imagery is another.
What it is that makes me put down a book is plot. I don't want a cliche plot line. This doesn't seem to be much of a problem for me, as I stay away from certain authors and genres. Also, styles and imagery; if the syntax is gray, or the word choice is putrid, or I find many cliches--I will put the book down immediately.