Polite Paradise

I avoided the Harry Potter books for years because the German cover art looks so boring and ugly. Eventually I found some English copies at a book store, which looked much more intriguing, so I started reading them and was positively surprised.
I later orgered one of the new books early and it came with a bookmark that had the German art style on it - with a picture that looked like a vomitting snake (I still have no idea what that was supposed to refer to, or who thought that was a good idea). I can't imagine how local children get into these books when they look like that.

On the other hand, I started reading the Hitchhiker's Guide to the Galaxy (and later the follow-up books) pretty much solely because it had metallic shiny art on the cover (and the pictures looked weirdly appealing without actually telling me anything about the plot). I usually read no science fiction and almost no comedy, but the short description on the back of the book sounded decent enough, and I turned out to love these books.
The cover art of the first two is still among my favorite.

I don't really know if it makes a difference to me if a book cover uses a drawing, paintig, photograph or even computer graphic. It's mostly about the colors, the overall look of it, and how well the chosen style matches the genre of the book.
I also have a few books that have no pictures at all on the cover. Fonts, size and color of the letters can also look more or less appealing.