Rick Yancey's Monstrumologist didn't give me nightmares, although it should have. It did have me scanning the road this morning looking for anthopophagi lying in wait, so I did see a skunk skulking across the road and managed to avoid it, all the while thinking "I can't outrun the monsters, but I need to go for their eyes. On their shoulders."
When a book bleeds into your everyday life, you know it must be effective.
Also very, very violent and scary, but it should be: In 1888, Will Henry, age 12, has been orphaned and is in the care of Pellinore Warthrop, a monstrumologist. When a grisly find is made by a grave robber, the two realize that there is a local infestation of a hideous, human-eating monster. After a local minister and his family are violently (and bloodily) killed, they gather their forces and try to kill off as many of the ravenous creatures as they can.
This is told as the journal of Will Henry, edited by Rick Yancy, so there is a forward. This is slightly too bad, because otherwise the first line would be "These are the secrets I have kept. This is the trust I have never betrayed." This writing is why I will buy the book. It is clearly horror, but the length (434 pages) and the difficult vocabulary will limit the interest to students mature enough to see beyond the blood and gore to the complexities of the characters. Yancey has clearly been honing his craft since the first Alfred Kropp. Descriptions are excellent, action and philosophical musings are well-spaced, and the characters are wrestling with their own histories and conflicts.
Just be aware that this is very gore-filled. I wouldn't have it in an elementary library, but if you have the Darren Shan Demonata series, this would be a good addition. Just be prepared to be looking over your should all day after you read it. Remember, go for the eyes.