I picked this up on a whim, initially thinking it was a book for adults with a cool cover. However, it's a children's book, and so I will rate it taking this into account.
The atmosphere of the book was quite good at times, particularly near the beginning. Furthermore, it deals with interesting themes of exploitation of the poor and vulnerable and truthfulness quite well. Nevertheless, I found that, while child abuse and alcoholism were quite large themes, these were not really explored as well as could have. Nevertheless, I found that the characters themselves were quite well-rounded, in spite of some of them being quite the stereotypical "Hagrid"-type strong but loving adult, and the old and wise man, etc. Still, I found Nathaniel an excellent character.
My main problem with this book, apart from its partial predictability which is probably due to me not being in the age range, is that the pacing felt quite a bit off. I was expecting the entire novel to go into the mystery of the ghost and what it wanted, but I felt this was a bit under-explored (though I found the descriptions of the ghost-experience quite interesting and well-done). Furthermore, I felt that the conclusion of the mystery, where they finally found out how everything was, was not done in the best way: I think the entire theory which turned out to be completely true on first guess was explored in less than two pages, before that it was kind of slow, and afterwards I felt everything wasn't even resolved propery, but rather very much rushed. Especially near the ending, when the main plot is resolved, I felt that it wasn't really rounded off and just immediately skipped to a moment much later.
This book had its positives and negatives, but I think the story in general would be quite entertaining, exciting and maybe a little but not too scary for a child. It seems to be quite a good but very mild introduction into more supernatural or horror-y tales.