Over on his blog the Critical Condition, Mark Blankenship did a post a little while back on what makes him stop reading a book. For him, the defining qualities are the smugness of the author and/or author overwriting. Yeah, I agree with both of those.
But I don't put down a lot of books. I support it, because as I said, life is too short to read books you don't like, but I like most books. Or...I like them enough to finish them anyways, especially because that usually doesn't take me very long.
For me, books I don't like fall into one of two categories:
1. books I don't finish (a very small category), and
2. books I dislike after I'm done with them ( a much larger, but still pretty small, category).
So what would make a book so bad (to me) that I wouldn't finish it?
a. Overwriting. I'm with Blankenship on this one. If you're too busy showing off your mad writing skillz (and/or you use the word "skillz" in your book) to tell the story, then I'm likely to put your book down. I understand the craft of writing, and I understand working hard on it, but I don't understand showing off.*
b. More important, maybe, than overwriting, is stupid characters. And my stupid, I don't just mean dumb. I mean dumb, and reprehensible, and annoying, and lame characters. This doesn't mean your characters have to be likable, but when they aren't going to be likable, then they better be interesting and not just thinly veiled ways for the author to justify wanting to bone a lot of women, RABBIT. ...not that I'm projecting or anything.
c. funny books. Not all of them (Hitchhiker's Guide to the Galaxy is fantastic, of course, and Lamb by Christopher Moore is pretty entertaining), but most of them. Because they aren't funny. They're groan-worthy. Or annoying. Or both. And usually the characters aren't actually characters, but just excuses for joke set ups.
* Some people are surprised, given my anti-show-off stance, of my love for Wallace and my disregard for Hemingway. But I don't feel like Wallace was showing off--I feel like he was writing in the way he needed to write to tell the types of stories he wanted to tell. And my dislike for Hemingway has nothing to to with his style.