I couldn't put this book down. It's well written, cleverly constructed and the setting in the woods, at a summer camp, works really well.  
Moore handles the different POVs and the jumps in the timeline (1950s - 1975) confidently.

The ending was nicely done - I liked the image of Judy leaving Barbara on her island in peace. Bear dying in an accident was surprising and elevated the the Van Laars to a whole new level of evil, esp. regarding Alice.  
Alice's tragic character (who we hear from as a narrator, too, in her drugged haze) is well written. It is clear she has given up and is numbing herself with pills and alcohol. -- Some reviewers have claimed that too many female characters are weak and victimised, but I disagree. Who wouldn't break, given what Alice is and was being put through? And Louise may be a bit cliched, but she isn't weak, just young, and we end with a very optimistic perspective.  -- 
It is the Van Laars I took issue with. They remain flat and elusive (which is due to the POV of the narrators. The only Van Laar narrator we get is Alice). This is a deliberate choice, and works very well in terms of the novel's atmosphere, and the whole point it makes about the divide between rich and non-rich. It works less well on the level of the mystery. It' such an easy out, "they did it because of their reputation". Especially because we know nothing about them, and their motivations... But well, you gotta cut somewhere, I guess. :)