My two cents:
I read "The DaVinci Code" and "Angels and Demons" because I wanted to give the author a fair chance. I hated them because I thought they were just very poorly written (kudos to the poster who linked to the posts in "
The Language Log").
One thing that people forget about writing is that it depends on a set of tools; we give these the general name of "language." And, just as we'd be unhappy with a surgeon who didn't know how to use a scalpel, or a mechanic who couldn't tell one wrench from another, there's no reason to be satisfied with a writer who doesn't know how to use vocabulary or punctuation.
This doesn't mean that books have to be all "deep" or "serious" in order to be good. They just have to be crafted with care and precision. I'm a literature prof., and happen to think that Stephen King is a master of his craft; I recommend his book "On Writing" to all my students.
So it's not a matter of being a snob; for me, it's the decision to not read books by someone who doesn't know how to use the tools of his trade.