Hell yeah, I judge a book by its cover. If the cover looks like crap, I'm assuming the story was written like crap too. I don't have to use the "Look Inside" feature to know it wasn't professionally edited, either. Life's too short and my TBR pile is too big to waste time on a book with a shitty cover. A good cover is more than well-rendered art, there's the matter of the appropriate font too. I've seen eye-catching art ruined by bad font, and I weep. Anyone trying to resurrect ye ol' WordArt should be shot from a cannon, FWIW. Bad font screams "amateur" and "badly written content inside."
Buuuuut, what about those covers that look like every.other.cover. in the genre? Are they bad for being too much alike? Ahahahah. Welcome to the wobbly line between delivering on reader expectations and trying to stand out in a listing of millions. Urban Fantasy covers tend to look a lot alike, and that's because readers identify that similarity with the genre so authors/artists deliver for the sake of sales (chicken->egg->chicken, yes). The core elements of a UF cover are:
- Hot chick (or dude) on the cover
- Magic representation (aura, array, shifter-sidekick, etc.)
- Urban-ish nightscape
- Weapon (8 times out of 10)
- A gun or a sword are the most likely, though there is an occasional dagger or crossbow.
On the other hand, Fantasy books--be they High, Epic, Grimdark, Hopepunk, RPG, etc.,-- have a wider pool of "typical" from which to draw. Some don't have people on the cover at all, it's mostly symbols and swirls. Some have the caped man in various landscapes. Some have brilliantly illustrated--straight from a graphic novel--look to them. Regardless of the composition, it's the quality of the art and the appropriateness of the font that matters. Fantasy readers are picky as fuck about quality. It's not a genre where DIY covers are a good idea (unless you're a professional designer/artist in your other life).
When it comes to using AI art on covers, keep in mind that most of the art produced by AI is stolen from artists and then remixed by algorithms; therefore, it doesn't have the appropriate commercial image licensing that's legally necessary for book covers. Yes, yes, yes. I know authors are publishing books with AI covers, but just because it's possible doesn't mean it's legal or ethical.