Oh man oh man, I loved this. I was a little nervous to read it, because I've loved basically everything Schwab has done, but I really loved this. Her writing is so beautiful and so perfectly fit this story of an invisible girl, forgotten by all she meets, throughout 300 years. 
Addie and her convictions are something I really connected with.  The ways in which she struggles but eventually finds her footing to adapt into the life she starts to live one she realizes she has all the time, ever. And in the beginning, her fear of running out of time, got me too, it's something I've always struggled with, especially on the days I find it hard to get out of bed. But if nothing could stop you, you could do it as Addie does, except of course, the catch that as soon as someone turns away, they will not remember you. 
Her relationship with the "shadow god" (I called him in my notes until the book named him), is also deeply interesting. Because of their deal, he is the only one who remembers her, but as the devil (?), he is fickle, only showing up occasionally to see if she is tired of life, only to find that she never is. Until, of course, Addie meets Henry, but spoilers! 
This is a book I never wanted to end, and yet I always wanted to know what part of Addie's story we would be told next.