One thing I've heard pretty consistently when talking to fans of the Weird series of books is that they love the cover design. I can't take credit for it, unfortunately, but I agree. It's simple, clean and eye-catching, just the way a book cover should be.
Sadly — no, thankfully — for every cover design that's great there are a dozen that are, well, not. And Nathan Shumate has assumed the task of compiling the best of the worst at Lousy Book Covers.