Posting a review of this book on Valentine's Day seems particularly appropriate, since a large part of the book is about love. The undying sort of first love that is made more poignant by the fact that the main characters in this particular novel are teens with cancer - and we are told from the outset that the narrator is terminal; she might live a while longer, but she's not going to pull through. (And yes, a female narrator is something new for John Green, and he pulls it off spectacularly well, since he appears to grasp that girls are, at the core, just people, the same as boys are, in many respects.)
The Fault in Our Stars tells the story of terminally ill Hazel, who meets a hot boy named Augustus Waters at the Support Group her parents force her to attend. Hazel and Augustus hit it off, and romance follows, even though Hazel tries hard to fend it off, believing that it's better not to form attachments, since she knows she's going to die, and she knows that the people she leaves behind will be hurt when she does, and, well, she doesn't want to be responsible for hurting more people than is absolutely necessary (and even then, as is the case with her parents, she wishes those people didn't have to be hurt).
Hazel tells Augustus about her favorite (fictional) book, An Imperial Affliction by Peter Van Houten, a literary sort of book that accurately describes what it's like to be a teen dying of cancer, and which ends mid-sentence as the main character dies or loses the strength to continue. Both Hazel and Augustus end up loving the book, and chasing down the reclusive author to try to find answers to Hazel's questions about what happened to some of the other characters in the book. Hazel is especially concerned about the main character's mother, wanting a happy ending for that mother. Without it ever being stated, it's entirely clear that Hazel is particularly worried about what will become of her own mother once Hazel dies, since her mother's entire life pretty much revolves around caring for Hazel - it's her mother's full-time job, pretty much, and as an only child, Hazel worries that once she's gone, her mother will be left with nothing.
There is a lot going on in this book - a lot of themes, including the aforementioned ones involving family and romance as well as an examination of what it's like to be sick in today's society, and how ostracizing it can be. The Fault in Our Stars deals with issues of love and of loss in a wonderful way (affirming that it is indeed "better to have loved and lost/ than never to have loved at all" (Tennyson), even though that quote thankfully never appears inside its pages). Instead of a book about coming to terms with mortality - and, to be fair, there is a bit of that here, but in a "causing the reader to think about the big issues for themselves" way and not in a "spelled out for you because you're too dimwitted to get it otherwise" manner, Green has crafted a story of dealing with the issues that life gives you, full of love (parental, platonic, and romantic) and of philosophy and poetry.
The book includes quotations of poems, including "The Love Song of J. Alfred Prufrock" by T.S. Eliot, "The Red Wheelbarrow" by William Carlos Williams, "Thirteen Ways of Looking at a Blackbird" by Wallace Stevens and, if memory serves, a bit of Robert Frost and Walt Whitman somewhere, although I couldn't readily find it. Quotations from Shakespeare (the title is drawn from Cassius's quote in Act I, scene 2 of Julius Caesar: "The fault, dear Brutus, is not in our stars,/ But in ourselves, that we are underlings") and from the fictitious novel by Van Houton, all of which tie into the plot and themes, sometimes in unexpectedly interrelated ways.
There are important conversations - conversations about what happens after death and whether there is such a thing as the immortality of the soul (that I totally remember having when I was a teen, if not in quite as articulate a way as Augustus and Hazel). Thoughts about Big Picture Things - the existence of God (or of some sort of knowing universe), what is it all about, why is there suffering, do you really need the bad things in order to appreciate the good, etc.
The writing is gorgeous - luminous. Numinous, even. The characters are human and real and have their faults and weaknesses as well as their strengths. They are angry and frightened as well as brave and noble. They are funny as well as tragic. And although there's a hopeful ending (yes, in a book that contains eulogies and in which you know for a fact that the main character is not long for this world, there's still a wonderfully hopeful ending), and although I already know that Tennyson was correct, the fact that the book hit me so very hard is a testament to the excellent writing and still more excellent ideas it contains.