It's not deep. The writing is kind of flat. The storyline is a bit predictable. But man, I seriously wanted to cry throughout the entire thing. 
 It's an interesting interpretation of the afterlife, that we go to this mysterious Elsewhere. We age backward, until reaching infancy, where we're returned to earth as a newborn. It didn't try to be religious; there was surpringly little mention of God (aside from, "He's around"). But Liz, our protagonist, is in denial that she's dead. It takes some time for her to accept "Elsewhere." 
 What really got to me was the reflection. When she views life back on earth, and the emotions go through regret, loss, and "what ifs," it tugs at personal reflection. I'll let you in on a secret: One of my biggest fears is regret. When Liz illegally contacts earth (in which most try to tell loved ones about their murderer, clues to their death, etc) all she wants is to tell her dad about his birthday gift. Because it was hidden in her closet, and she feared he would never find it. I just about lost it. 
 It's about growing up (ironic, since you essentially "grow down"), moving on, and accepting things as they are. This isn't something we should wait to learn about in the afterlife.