It's true that covers—especially in genres like romance, action, and mystery—are not primarily designed to illustrate the book or to be aesthetically interesting but to convey what kind of book they represent. Shopping for genre novels is often a guessing game, especially when it comes to romance: The novels aren't widely reviewed in major media outlets, and personal taste plays a much larger role in a reader's enjoyment. So readers rely on clues like covers, descriptions, an author's reputation, and reader reviews—scanning for telltale phrases like "great story," "fast-moving," "in-depth characterization," "too much sex" (meaning for many of us "just the right amount"), and so on.
Covers are kind of the first winnowing tool in this process. First, it tells you the subgenre at a glance. Here we've got historical, contemporary, and cowboy subgenres:
Twilight and 50 Shades of Grey ushered in a wave of good design for contemporary romance, one that features meaning-laden objects rather than settings or people:
Contemporary romance novels have benefitted ever since, and Courtney Milan's Trade Me is clearly the best design of that first group—and pretty typical of contemporary covers.
Second, the cover gives you a clue as to quality. I'm much more likely to pick up this book:
than this one:
(Note to newbies: Outlined text on a cover is ALWAYS a bad sign.)
But Grace Burrowes's The Laird—which is quite a good book—still harkens back to the cheesy Fabio era of romance covers. And featuring faces on a cover is always a risk. This guy? Maybe:
These guys? Uh-uh. I don't care how good the reviews may be, these covers are flat-out boner killers:
Following the principle of "Do No Harm," I'd much rather have an old-fashioned scenic cover than any of the above since at least these covers are weak and unlikely to have any psychological impact on my reading. Laura Kinsale's Flowers from the Storm is a good example:
Still, I don't think you'd get from this cover what an incredibly good writer Laura Kinsale is—or that Flowers from the Storm is repeatedly voted one of the best romance novels of all time. Kinsale is an interesting case, actually. A super good historian as well as writer, her novels have been reprinted enough to go through several iterations of cover design. Here are two of her novels in their earliest form:
Flat-out awful (outlined type—blech). Then came these editions:
Better. But in the last few years, her covers have made a exponential leap forward. I cannot think of any other historical romances with covers as arty and intriguing as these:
Or these, from a different series:
And now there are audiobook editions:
These are damn good covers. As romance continues to gain respect and a new generation of smart women tout its virtues, here's hoping there are more to come.