The Hunger Games is a series of three novels - the first gives it's name to the series, followed by Catching Fire and Mockingjay, and all three follow a similar structure of about half a book of setup followed by half a book of arena-based slaughter, even the final one, which is dedicated to a Revolution against the state. Actually I think how Mockingjay works this in is quite clever, compared to Catching Fire's more predictable "do-over" format but perhaps that is skipping ahead a bit. The basic premise is pretty simple - in "the future" society collapsed and what was once the United States is now "Panem", ruled by The Capitol and consisting of 12 Districts under it's rule. Due to a big revolt many years before, The Capitol has ruled that each year two Tributes from each District must fight to the death in a big, artificially controlled arena for the televised entertainment for the masses and to prove who is charge. Tributes are usually chosen by lot, although our narrator, Katniss Everdeen, volunteers when her younger sister is picked.
It's a fairly simple and straightforward plot - in fairness all three books have fairly straightforward plots - but the strength of them is the depth of the world building and Katniss' narrative voice. She starts emotionally withdrawn, suspicious of the motives of others and riddled with self-doubt, and only gets worse as the series progresses. There is an element of the old Trope that the heroine doubts herself but is constantly being told how wonderful, and beautiful she is, but on the whole it makes I found that it undercuts the other potential issue that she is pretty damn competent and clearly inspires the best in others.
Katniss being the narrator is also used to muddy the waters and keep the reader in the dark. In many respects - or at least to someone who is over twice the age of it's target demographic - this is a pretty predictable story but if often you're in the dark as much as Katniss over some characters motivations and actions, although in this is the big weakness of Catching Fire, where I was sufficiently "ahead" of her that she just started to look a little bit stupid. It is however used to great effect in Mockingjay as her mental state starts to deteriorate, and the book becomes half revolutionary action drama and half psychological study into Post Traumatic Stress Disorder.
So there is actually quite a lot going on here. It's pretty violent, a lot of people get killed and it's not always on the good guy / bad guy alignment. As you'd expect from a work aimed at teenagers there are lot of distant or untrustworthy authority figures that can't be relied on, but enough help comes from unexpected places - usually because Katniss has misjudged a situation - that the story throws up enough curves to stay interesting. I do think the rulers of Panem needed to invest in a copy of "Totalitarian Dictatorship for Dummies" though, as many of their schemes fall under the label of "cunning, but stupid".
In the final analysis I really enjoyed the series, which unfolds and changes in a slightly predictable but consistently fun way. It manages to balance a necessary darkness with hope and a touch of bleak humour, and is well written and paced. Whatever genre label you put on them, they are just properly good books.