Actual Rating: 4.5 stars 
 Opal is probably my favorite book in the Lux series so far. I loved Obsidian and I mostly enjoyed Onyx, but I loved this book! There's something about Jennifer L. Armentrout's writing that is compulsively readable. I'm almost never bored, and I love the characters she creates. I'd really like to look into her adult novels at some point, because she is definitely going on my favorite author list. 
 I loved Opal much more than Onyx mostly because of the lack of love triangle in it. Honestly, I just couldn't stand Blake for most of the book, and I still can't. I don't hate him, I guess, but . . . well . . . no. Actually, I do hate him. And at least 60 percent of Onyx was Katy making stupid decisions regarding Blake and somehow managing to even think about another guy with Daemon around (really, how is that even possible?). But in Opal, Katy and Daemon were finally together and acting like a real couple, and it was great. 
 I love how each of the books corresponds to some kind of stone or gem - though I guess, the fourth book, Origin, probably won't be like that. I think the whole plot is pretty creative in general. I didn't even think I would like these books before I read them because I've never cared much for most stories about aliens/space. But I'm hooked, and now I need Origin in my greedy hands, like, yesterday. 
 That. Ending. What kind of a person is so cruel that she leaves readers with that kind of ending? I am still trying to process it. I eagerly look forward to seeing how everything works out for Katy, whom I suspect may go through even more changes by the time this series is over.