One thing I’ve learned from moderating a mystery book discussion group for writers is that few crime novels stand up to close inspection or even a second reading for pleasure. More than once I’ve recommended a book to the group because I loved it and thought we could learn from it, only to discover during our detailed (and merciless) discussions that I don’t admire it that much after all.
You might think this happens because a mystery or suspense novel – any novel, actually – is an artificial construct, with the clear beginning, middle, and neat ending we seldom see in real life. The more closely we look at a novel, the more unreal it seems. That certainly has an effect, but it’s not the only reason why books we love can disappoint us on a second reading.
One explanation is that people change but books don’t. If you read a novel for the second time a month after the first, you will be a marginally different person and might see some flaws you missed initially. Wait five years and your interests and emotional life might be so different that you wonder how anything in that book could have pleased or moved you.
The books we never grow tired of, the ones we label “classics” – Jane Austin’s novels, for example, or the works of Mark Twain and Charles Dickens – stand up to repeated readings or viewings as movies or TV dramatizations because they tell universal stories that touch us regardless of where we are in our own lives.
To Kill a Mockingbird is widely regarded as the greatest American novel ever written, and it continues

copies every year. I have read it more than once and seen the movie more than once, and I doubt I’ll ever tire of it. But each time, I’ve seen it in a different light because I’m a different person. Sometimes I’ve identified with Scout, at other times with Atticus, and for a while, Boo Radley was the character I felt I had the most in common with. Mockingbird is a perfect novel – beautifully written, cleanly structured, with characters and a message that transcend time and place. The story makes sense, however many times you read it.
Few books have all of those virtues, and the mystery genre, like romance, is the home of many novels that are intended to entertain and quickly be forgotten. If you read them a second time, your emotions won’t be fully engaged again, and your mind will rebel against any clunky writing, questionable plot turns, shallow characters, and weak motivations you overlooked (or noticed but forgave) the first time around. Just as few novels have all the virtues, few have all the flaws, but most books have some of them.
In discussing crime novels, a major problem my group often sees is weak motivation. I’ve been surprised more than once, when re-reading a novel I enjoyed the first time, to discover the characters have little reason to behave the way they do. This flaw comes hand in hand with weak characterization. The character might be vividly depicted, we might be able to “see” him or her clearly, but if we don’t understand the person’s inner life, we can’t understand why an apparently sensible human being is doing dangerous or hurtful things. Without that understanding, the plot won’t make sense. Why didn’t I see the flaw on the first reading? Maybe I liked the writing style or the atmosphere or the suspense and let those elements blind me to the problems.

As for my own published books, in the course of rewriting, editing, and proofing, I've read both of them so many times that I'm thoroughly sick of them. I know what their flaws are. But if you read them only once, maybe you'll overlook the flaws -- or at least not mind them too much.
Have you ever read a book a second time and wondered why you liked it the first time? What is most likely to disappoint you if you look too closely – plot, character, writing style?