I'm going to start with a preamble because this is probably one of the more conceptually bizarre books that I've ever read and much of what I go onto to say really needs the context: 
 In Rainbow Rowell's novel Fangirl we met the character of Cath, whose major hobby was writing slash fanfiction for a Harry Potter-style book series called "Simon Snow". Simon is a boy wizard at a magic school and part of an adventuresome trio of teenagers. His bitter enemy, Baz (think HP's Draco), is also his roommate, and in Cath's stories the pair fall in love. Carry On is Rainbow Rowell's attempt to write her own version of that story, effectively creating fanfiction for her own fictional invention. 
 (Confused yet?) 
 Which all leads to the question, "What sort of book am I reviewing?" Is it a fantasy novel? A fanfiction pastiche? A teen romance? Judging the book on any of those terms seems to produce wildly different answers - for me at least. The part of me that read Harry Potter fanfiction when I was younger happily plowed through this book. The part of me that reads and writes modern fantasy was giving it some serious side-eye. By the simple criteria of "did you enjoy it?" - I had a blast. It was inventive and touching, a big bold fantasy novel with a gay teen romance at its heart. Carry On played around with the archetypes found in novels like Harry Potter (which I also love), subverting and recasting ideas in such a way to make you consider those stories anew. But. 
 But. 
 As a novel, I just don't know how it all stands up. Given that Simon Snow is a Harry Potter analogue, the book begins as if we are reaching the end of a sprawling epic. In Fangirl, "Carry On" is equivalent to the eighth and final book in the "Simon Snow" series, and this novel reflects that by starting at the same point, as though seven books' of character and backstory have come before... Except it is in fact a standalone novel, and those previous seven books don't actually exist. As such, the author is attempting to write a thrilling final installment, whilst frantically backfilling all the setup that we're missing. She's not helped by the fact that her original worldbuilding, when she sets round to doing it, is horrendously clunky. 
 Rowell's solution to this (and part of the reason for my inner-fantasy reader side-eye), is metatextuality. 
 For example: at Watford Academy (not!Hogwarts) Simon is friends with the "goat herd" Ebb, who lives in a small cottage on the edge of the grounds. Sound familiar? Anyone who knows Harry Potter sees that this is analogous to Harry and Hagrid's friendship. Rainbow Rowell can give us those very few details and then run with the scene, assuming that her readers will get what's going on by dint of the backstory that they bring to the text. It's a clever solution to the structural problem, and she avoids being entirely vampiric in this by engaging with the resultant reader expectations. You assume that Simon's relationship with "the Mage" is going to be rather like Harry and Dumbledore, and then she subverts those assumptions - hard. 
 So by no means is this a sorry case of plagiarism, but the decision does also lead to a certain thinness in the characterisation (and in the worldbuilding... and in the plot...). It feels a little similar to reading satire, where a writer might take advantage of certain archetypes in order to lampoon them. Sir Godber in Porterhouse Blue (for example), is drawn broadly enough to stand in for any dull, cautious career politician that a reader might think of. Caricature makes a fine basis for humour, but Carry On is conversely striving to be romantic and epic, and I think this is where my problem lies. A month and a half after reading this book, I find that it has left very little impression upon me. 
 Another example: Central to the notion of the Simon/Baz romance is the fact that they've hated each other for seven years; animosity masking sexual tension, etcetera, etcetera. But Baz is kept off-page for the first half of the novel, and we are simply told, repeatedly, that they hate one another. The only reason that I, as a reader, bought their relationship (and its romantic turn), was that I have read Harry Potter and thought to myself, "Okay, so they have a Harry/Draco dynamic". So the romance plotline worked for me - it was sweet, touching, and most importantly a gay fantasy teen romance from a major publisher, but it also felt strangely vampiric. As if Rainbow Rowell was telling me the punchline to somebody else's joke. Which is not to say that the metatextuality is bad, but that I think it allowed Rainbow Rowell to write a very fun book, which doesn't quite manage to justify its existence on its own terms.