It takes, Diff'rent Strokes to move the world.
(Ahahahaha. Like that, Kelly? --->)
So, in an epic (<---that might be pushing it) coincidence, Kelly at Stacked also wrote about Then You Were Gone yesterday. And she enjoyed it much more than I did, so I'm just going to point you over there for an extremely different take on the book.
And I will ALSO point you in the direction of some of the conversation we had about it on Twitter last night—the two longest threads are here and here—along with Karen from Teen Librarian Toolbox.