The book is 176 pages long with most of that taking up the screenplay, which means if you want a crash course in how the creator of Buffy writes descriptions, here it is. But the photographs are gorgeous. There's stuff on the creation of all kinds of amazing (and occasionally truly grody) effects and creatures the very existence of which would be a major spoiler. Totally recommended-- but don't flip through this if you haven't seen the movie yet!
Speaking of things not to read if you don't want to know what happens but perfect if you do or already have, I also got the Cabin in the Woods novelization by Tim Lebbon, a Stoker Award winner who has become the go-to guy for turning creepy horror cinema into creepy horror fiction (Lebbon also wrote the NY Times Best-Selling 30 Days of Night book.)