Don't compare this to The Hunger Games, first of all. This genre is bursting with good futuristic altered-American-reality books, and this one is fantastic. Yes, it is a movie, but of course the book should be read first!
Divergent focuses on Tris, a girl who must choose, as everyone her age must, which of the four "factions" in their society they would like to join. It is most common to stay in your family's own faction, but switching is not unheard of. When Tris finds out during her screening test that she actually has the skill or inclination for three different factions, she learns that she is actually "divergent," a label which could get her killed! She decides to leaver her straight-laced Abnegation faction for the thrill-seeking Dauntless, and through many hard times, she learns that she is, though small, a natural fighter.
Though Tris is enjoying her new freedom and faction, she soon learns that there is a plot afoot that could destroy everything, and it is up to her and a few trusted friends to save the day. As family, friend, and faction are shaken, shocked, and turned against one another, Tris realizes that nothing is as it seems after all. The adventures of Tris are incredible, exhilarating, and heart-wrenching, and you will not be able to put this book (or its two sequels) down!
This is really a TEEN book, because of the violence, love scenes, and more mature content. That said, the fifth graders who have read it seem to have no problem with those parts... Perhaps we parents and teachers worry too much? Or perhaps children today have been exposed to more than is good for their young minds and are not surprised by things that should shock them. I can't say, but I would recommend young (elementary-age) kiddos to get their parents' approval before reading this one.