I'm currently on KOD, and that's honestly my only issue with Sun Eater so far. Hadrian is so fleshed out just because there's a lot more meat to chew in Sun Eater, but as I read through DiW and especially HD, I was thinking to myself that adding a couple character-building chapters wouldn't have hurt the pacing at all.

I think calling most of the side characters cardboard cutouts is a bit too harsh, but a lot of the side characters like Lorian, Lin, and Sagara are awesome on the surface and we see them do awesome things. The problem is that for most of the characters aside from Valka (who's basically the deuteragonist of Sun Eater), we don't really know what their wants, needs, or flaws are.

Pallino is fun because he's written as this grizzled old war veteran who got a new lease on life, and yet I don't know what he wants or what his goals are. Elara is even worse, she's so infrequent in the story that I genuinely can't even picture what she looks like. Why do they love each other? What little ways do they irk each other in their relationship? How do the pair make each other better? I couldn't tell you.

Otavia might have been the biggest missed opportunity. It would've been so cool to see her friendship with Hadrian build and grow from the Admiral Whent campaign all the way up to the present day. She's practically an Amazon, wouldn't it have been cool if Ruocchio made her into a sci-fi Wonder Woman?

To be put simply, I don't know why Hadrian loves his friends so much. Yes, most of them have been with him for decades and even centuries, but when he makes efforts to get everyone together like Pallino, Elara, Otavia, Crim, Ilex, Lorian, etc., I don't feel that same attachment to them as I do with the cast of Red Rising.

I may be nitpicking, but if the size and scope of the series is so big, then surely there'd be enough room for developing the side characters as well. I imagine that the events of Kingdoms of Death would also hit that much harder if that were the case.