Judge a book by its cover... please.
When we are young we are told not to judge a book by its cover, but growing up to become a graphic designer, that's exactly what we want people to do.
A book cover is designed to give you a glimpse into the content of the book, and the world that it creates within its pages. The job of a designer is to capture this world through colour, imagery and typography to bring the author's vision to life.
Sure, there may be some super interesting books with some pretty questionable covers. But delving deeper into these covers can reveal some pretty clever concepts present throughout the book.
Or not, but that's your call to make.
Utilising the themes of a book within the cover is something I feel is important to convey the content of the book effectively, and therefore make judging by a cover totally okay. Because if the cover is accurate then you can accurately judge whether its suitable for you or not.
The idiom, "Don't judge a book by its cover" metaphorically suggests that we should not determine the value of something or someone based on its outward appearance alone.
In terms of people, I strongly agree.
However, in a more literal sense, I would definitely encourage you to judge that book by its cover, on behalf of the sanity of designers everywhere. Beyond the surface lies blood sweat and real tears in an attempt to grab your attention, so embrace it.
Get judging, run yourself a bubbly bath then get reading.