Hands down, cover art sells books. The better the cover art, the more a book sells. The downside is that it also raises reader expectations. I've picked up some books that have had outstanding cover art, only to be seriously disappointed.
I know some writers who seriously wished they could have picked their book cover artists. Cover artists don't much care, to an extent. They get paid a flat raid in this business. But I'm sure there have been some artists who got really embarrassed over some of the books they've been on.
But I digress. I love the cover above. It's a basic black and white shot of an interesting, aggressive female in a spooky fog-shrouded forest. Love the big tree with added copy stuck on it. And that's interesting because if the copy hadn't been there, the tree would have balanced the woman out and been distracting. We the copy on it, we kind of ignore the tree because the copy pushes it back into the background once you've digested the message.
Then there's the mixs of colors (orange and green) which don't always go well together on book covers, but in this case serve to bring that "dead" looking forest to life a little by warming up the page.
I like the author and picked up the book based on past reads, but that cover would have sold me even if this had been someone new.