Not bad. It felt more like three very short books that got rolled into one, as opposed to a single flowing narrative, but I enjoyed all three parts, so it was only minorly annoying. The writing was decent, the worldbuilding was fun, if not very detailed, and the characters were passable. Very standard and unsurprising, but nothing objectionable. There were a few points that made me side-eye, like when Tier quite clearly forces a kiss on Seraph, and it's presented as a "well, of course guys have to force a girl, because she's not going to admit she wants it until after he's already snogged/fucked her" feel to it. One of those scenes that I think snuck in there from the author's subconscious, but then again, subtle scenes that get passed without objection are how cultural trends spread and take root. But if you keep an eye out for that stuff, the rest of it isn't bad.