I'm a bit tired of the "dude/dudette with a cloak" covers that seem to dominate fantasy covers (both big 5 and self published). I understand why they're so popular: they let the reader know it's a fantasy novel that will likely have some intrigue and skulking in shadows; they create a dark, moody feel; hooded cloaks are flexible and ubiquitous enough garments to fit into a wide range of periods and settings; and they tend to hide specific features like hair color, build, facial features, and even race (and sadly, this last is often done intentionally).
But they've become such a cliche. I'm not crazy about half dressed women, women in tortured body poses, or women in completely impractical armor on covers either. Don't some publishers know that most fantasy readers are not teenaged boys these days?
Another thing I tend to dislike are covers that are too busy, perhaps because the artist wants to include every major character or exactly reproduce a scene from the novel. Less is often more with cover design. It's not good if a cover makes me go, "WTF is that supposed to be?"
Some personal things that tend to make me scroll past would be covers with a protag in leather pants and a modern cityscape in the background, because UF isn't generally my thing. But this isn't a design flaw so much as branding, and it probably lets people who do like UF know what the book is.
However, the biggest deal breaker is any cover that makes it immediately obvious that the book is self published and the writer didn't get a cover that was professionally designed by someone with background in cover design.
Here's the thing: I have a bias against self-published books. I've read and enjoyed some, but the market is flooded with un-edited, cobbled-together, poorly written offerings, and I've got a huge stack of books waiting to be read on my e-reader and night stand. I tend to stick with trade published novels for this reason, unless I know the author or have heard many good things about them. And if I stumble across a trade published novel while browsing (or one pops up on my recommendations list), the only way I'll likely check it out it is if it's so professional in its presentation it fools me into thinking it's a "real" book of comparable quality to what the big five put out (and by the time I realize it's self pubbed, I'm intrigued, so I give it a try).
So I will not peruse anything that looks like someone designed the cover themselves with programs like Poser or Photoshop, or that someone relied on their own or a friend's un-professional talents with crayons (seriously, how many trade-published novels for adults have crayon drawings, no matter how well done), or a cover that looks like someone purchased the rights to a nice enough piece of artwork via deviantart or some such site, abut they just slapped it on and randomly picked a font without any understanding of how to make the composition work as a book cover.
Still good info. and great to add to. Langadune, I'm still not sure, since it about cover design. I sent a message to the bird to find out. The post was left 3 months ago, hopefully birds have a long memory. 
