So we often do a lot of discussing of cover art here, and on occasion I've been accused of missing the point or obsessing over unimportant details in this regard. I'll admit, we've got a lot of cover commentary and discussing going on. I mean, pretty well every review has some form of cover commentary in it, and I have a
fairly well-used tag devoted to posts talking about cover art.
So... yeah, ok. Maybe a little obsessive.
The thing is, though, that cover art is important. Yes, of course we buy books to discover the story between the pages, and it's a tragic truth that unless they self-publish, an author has no say at all over what goes on their covers. But the cover art combined with the title make our first impression of that book, and unless it's something written by an auto-buy author or something that's come highly recommended from a trusted source, it's what we have to go by to catch our attention and lure us in. In that way, it's an important part of the book, and the marketing people know this. The major publishers have entire departments devoted to this, and they put careful thought into how best to present the book to people, using visual shorthand and (hopefully) appealing images to convince potential readers this is a book they want to pick up off the shelf. There's nothing accidental about the covers of these books; they're very deliberately concocted to create the message the advertising team thinks will sell the most number of books. They're giving us what they think we want to see, and that should be held open to criticism, especially when what they're giving us is not what we want to see, as in the case of blatant sexism or racism, both of which are distressingly common on cover art.
Does the cover art affect my enjoyment of the story the author has written once I start reading? No, I can't say that it does. But it's part of the package of the book, just as much as typography or frequency of typos, which are both frequently commented on in reviews. Let's be honest, we've all picked up a book based on the cover, at least inspired to give it a closer look, even if we haven't purchased it solely on the strength of that cover art (and, well, a few of us have done that, too). It gives us certain expectations before we even start the book, and that can colour the reading experience.
So basically, I criticize and comment on cover art because I think it's important, because I think it's relevant, and because I think it's a subject that just doesn't get touched on enough. It's not just snark (although snark is certainly fun); it's just another aspect of book critique, one that's frequently glossed over or ignored.