Mary Roach's first book, "Stiff," is one of my favorite non-fiction books of all time.  It has earned a permanent spot on my bookshelves, and if you know what a fanatic I am about decluttering and "culling the herd" and selling old books to buy new ones, you would realize what a place of honor that is!  I have to admit that I didn't enjoy "Spook" quite as much as I enjoyed "Stiff," but it was still a great read.  
"Spook" and "Stiff" both belong to the category I call "narrative non-fiction."  Non-fiction as a whole encompasses everything from cookbooks to illustrated books about fighter plane models.  Narrative non-fiction is a sub-set of that, which can be about almost any topic, but follows an essay style similar to what you might find in Harper's or the New Yorker.  The "I" is very present in this category, which also tends to be chatty and filled with asides. David Foster Wallace (RIP) was the king of narrative non-fiction, with essays like "Consider the Lobster" and "A Supposedly Fun Thing I'll Never Do Again."

 "Stiff" belonged firmly in the science category, being all about the actual things that happen to your body after you die.  It thus had a patina of educational content, but more than that, it clearly impressed Roach herself.  Narrative non-fiction is as much about the narrator as it is about the topic, and Roach's enthusiasm and curiosity shone through every sentence in "Stiff."

Alas, Roach clearly doesn't find the topics and kooks of "Spook" to be nearly as impressive as those in "Stiff."  Part of the problem, I suspect, is that a lot of the essays in "Spook" are about historical topics, and involve Roach turning pages in books and tattered nineteenth century newspapers.  With a few exceptions (waiting to unwrap "The Alleged Ectoplasm" at the Cambridge Library; sitting in a 70's-décor experimental chamber to be bombarded with infrasound), Roach isn't personally engaged in the events.  

The good news is that this is still an incredibly entertaining book, even if its topic - ghosts, the afterlife, whether or not it's possible for a soul to have weight or individual agency - isn't what you would call "respectably scientific."  Roach is an excellent researcher and writer, and an admirably skeptical author in an age when it sometimes seems that skepticism is on the wane.  Reading some of the kookery she dredges up from the past, I couldn't help thinking about some of the kookery that goes on today, seemingly unchecked.  

If I would have preferred more modern-day topics and fewer historical ones, the historical topics do help put things into perspective.  That being, basically, that everyone has always been crazy and credulous, and probably always will.  The deck is stacked against rational thought, but it's still important for authors like Roach and others to fight the good fight.  And, in the case of Roach's writing, it's funny and entertaining, too.