Mendacities is a very, very entertaining book, let's make that clear. What's less clear is how to describe it; it's a novel about a group of high-school students (which makes it by some definitions a YA novel), one or more of whom attempt to develop plot-related same-sex relationships (which may or may not make it an LGBT novel), all of whom uncover the answers to a sinister political mystery, become embroiled in a real-life conspiracy theory, and get caught up in some relatively zany adventures (which may or may not make it an adventure novel). After various adventures, including a homicide or three and some gently science-fictional elements (which may or may not make it an SF novel), a slightly audacious resolution is reached which leaves the main characters older, wiser, and more cynical (which may or may not make the book a coming-of-age story). Also, there's a romantic subplot which achieves a happy resolution, some gentle philosophical moments, some brief casual nudity, and probably some other things I'm forgetting.
Unless you consider "romantic LGBT YA SF dystopian political conspiracy coming-of-age adventure novel" a genre, where to shelve Mendacities might be a problem. The author suggests this is actually intentional, in that he was trying to emulate a Japanese "light novel". As far as I can tell, being no expert in this field, he succeeded admirably. Not having a shelf for light novels, my copy lives among my (other) favorite trade paperbacks - by the likes of Neal Stephenson, Lois McMaster Bujold, and Robert Lynn Asprin. Make of that what you will.
The author suggests that Mendacities is suitable for "ages 15 and up, more or less", and I believe this is basically spot on. There is a small amount of violence, yes, and some underage drinking and casual nudity, but it's all handled quite soberly, rather than glorified in any way, and in the age of MTV, HBO, and the Internet, I really can't see how anyone could find this objectionable for anyone age 14 years and above.
Rated four out of five stars merely because world-building and character-development fill the first three (entertaining, and foreshadowing-rich) chapters before the real plot actually comes along.