This is going to a very straightforward review if you read The Hunger Games. Take your impression of that book and apply it to this one. Red Rising has a different setting and characters, but the plot is similar and the underlying theme is a carbon copy.
If you haven't read the Hunger Games, then the novel is, at it's core, a coming of age story with a science fiction veneer and a whole lot of violence.
A good read to munch down on if you aren't interested in reading something complicated.