First of all I liked the documentary style the book is written. It gives a certain touch of credibility, like you were reading an actual report of the event.
Secondly; using children as the base horror, even though some might find it clishé, is creepy and that gives a nice shiver to the story. So bravo on those.
But. The end solution of the Three didn't quite satisfy me. I'm a big fan of Stephen King, so I don't mind if there are few loose ends and stuff you have to figure out you own at the end, but Lotz seems to leave quite a lot speculations for the reader to decide what actually happened. And why.
Other than that The Three is quite good & fast paced story, slightly creepy, but didn't make me leave the lights on for the night... ;)