Red Rising was quit an interesting mix of ideas and concepts. We have a bit of a Hunger Games concept mixed with a dystopian science fiction beginning. Lots of mythological references and genetic engineering or planning births to achieve certain results.
Darrow is a red - the lowest color. And as such, he is relegated to mining underground for his entire life. But part of his spirit rebels and send him on a very interesting journey. His journey is a strange mix of sci=fi and medieval technologies. We don't get to see the space battles with ships and stations - but they are still an obvious part of the world.
As Darrow fights to bring chaos to the rulers of the galaxy, he is forced to learn a lot about himself and human nature. This could almost become a study in psychology and sociology. There are tons and tons of twists and turns throughout the story and there are quite a few times we think Darrow isn't going to win.
The end has a lot left open (this is a trilogy) but I wouldn't really call it a cliffhanger.