The worst book ever written. John green could could write a book that as soon you open the first page he comes through a door behind you and shoots you in the head with a shotgun, and it would be a far more enjoyable reading experience.
Seriously though, Hazel is the most unlikable character I've ever read in any story. All you need is one or two more hints and you could have retitled it "The inner thoughts of a psychopathic narcissist". And then the dude dies instead of her, really, what were you thinking. Read 1984 instead.