I don't think Dark Age is my favourite book in the series, but I think it's the one that has stuck with me the longest, and with the most intensity. Since finishing it, I have re-read the original trilogy, re-read it again, and started contributing to this wiki.
On my first reading I think my strongest impressions were of emotional impact. It left me feeling quite down, probably coupled with everything else that's happening in the world right now. It's not a very hopeful book that inspires. And I really hope that the message of this second trilogy doesn't end up being that fascism is inevitable. Pierce generally seems to have a good head on his shoulders, and seems to care about inclusion, so I think it's unlikely.
My second impression was that I found the violence, particularly the sexualised violence, a bit much. I suspect it's very much the point. I've never been a fan of gore/horror as a genre, or extreme gratuitous violence. I find it particularly hard to stomach when it's used for shock value, because it has to keep escalating. I feel like Dark Age walked a thin line in this aspect (Silenius razor if you will).
Even with all that I find myself incapable of tearing myself from the Red Rising universe. It's this very nice mix of so many other things I enjoy. A lot of the wargear and tactics feel very Warhammer 40k, and Ephrahim's whole story in Iron Gold was like a Shadowrun campaign. And the setting has so many interesting avenues that could be explored. We still know very little about Greens, Whites, or Yellows. I doubt Pierce will be able to explore it all, but I'm hoping that the universe itself will expand, with more players being able to tell stories inside of it.