I waffled between rating it 4 or 5 stars. Call it 4 and a half, rounded up for holiday good will. It's "fanfic" based on a fictional series of fantasy books that serve as the focus of fanfic for a fictional character in a YA novel by the same author. A bit confusing, yes, and I do think you have to read (& like) Fangirl first to be able to appreciate Carry On. At first, I didn't particularly enjoy being thrown into what felt like the final book of a long, complicated series with only the barest background provided by Fangirl, but by the end of this book that feeling had dissipated. And even though it is clearly influenced by Harry Potter -- or more accurately, by the phenomenon of Harry Potter and the fandom that it and similar books have spawned -- I don't think anyone will mistake it for Harry Potter fanfic. (Especially since the ending is not nearly as disappointing.) I'm happy I bought it & will recommend it along with Fangirl as a pair for all YA-SFF fans.