I'm not all that surprised to have this overwhelmingly positive response to Green's work, as I've read all of his other books and had similarly contradictory feelings of joy/sadness (is this melancholy?) at various points of those books. Green had worked in at least one hospital for young people earlier in his life, and I think the raw experience shines through honestly in the most powerful dialogue and narrative points of this one. Green's gift for crafting characters that I always care about and feel like friends, combined with the real life experience in the hospital puts The Fault in Our Stars right up there with his best work.
It's still much too early in 2012 to start a best of list...but I don't see myself forgetting this book later in the year when listmaking time comes again.