I came to read The Book of Lost Things after having read Mr. Connolly's The Gates and The Infernals, both of which are considered young adult, so it took me a couple of minutes to reorient myself to the fact that this book is very much not a children's book. 
 The retelling of myths and fairy tales (of the Grimm/grim kind with very adult lessons and descriptions and allusions) is handled very nicely. Yes, some of the reworkings might have been somewhat expected in their 180 degree turn about (view spoiler)[such as: Red Riding Hood seducing the Big Bad Wolf; Snow White being quite the opposite of fair, skinny, and a great catch for any prince and instead being lazy, obese, and loud; and the journey of a disgraced knight (Roland) searching for his lost love... another knight. I read it more as bringing society's current--and some older, in keeping with the WWII era--fears into the fairy tales just as earlier storytellers did. We might think we're modern, but things like sex/sexuality, loss, and change still are things that scare us. (hide spoiler)] 
 Overall, I greatly enjoyed it.