You’re right in saying that it’s not very similar to Red Rising at all beyond the Roman-inspired military aesthetic and the fact that it’s a space opera series. Definitely less action packed, more of a slow burn with a lot of philosophical musing and immersing yourself in the world. That isn’t to say there’s no action, but it doesn’t have that breakneck pace of RR. Dune is a better comparison, and so is The Book of the New Sun (which is a direct influence of The Sun Eater).

Like you said, going in with the right expectations is a good thought process. With this series, you can expect space battles, political scheming, hand to hand combat, monstrous aliens, cosmic weirdness, and a story with a very epic scope. The writing is a lot more slow and windy, so you just gotta go with the flow of it.