All right, so I said it with the first book - I know the rumors. It's why I'm so frustrated with this series right now. 
 I happen to believe that Monomyth is a true theory. It's also called the 'hero's journey' which essentially argues that there is a particular story arc for any plot featuring a hero. Basically the hero goes from what he/she thinks is an ordinary life to something of a supernatural wonder. The hero forges through a quest to a victory, ultimately changed from the adventure. 
 We see this arc all the time: Star Wars, Harry Potter, Lord of the Rings, and so forth. It often times has bothered me how people argue Harry Potter is just Star Wars with light sabers and dismiss all the original creativity that went into the books. The generic story arc existed long before Star Wars and most classics derive from this plot. 
 I think the same can be said for most paranormal young adult today. Ignore it all you want, but there is a generic story arc that is being used for most of these books: Twilight, Divergent, Hunger Games, etc. 
 Is Armentrout guilty of using this arc? Absolutely. Is she guilty of plagiarism? Oi. I just don't know. 
 Onyx felt far more original to me than her first book. Katy and Daemon are trying to figure out their relationship while dealing with the DOD, the organization that maintains the secrets of the alien race and ultimately can decide their fates should they prove to be out of control. 
 After Daemon used his powers to heal her, they forged an unbreakable bond. Now, Katy must deal with her own growing powers as she deals with being a mutation, all while trying to balance her teenage life. Meanwhile, a new boy in town shows a serious interest in Katy, forcing Daemon to reveal his own feelings far sooner than he wanted. 
 This book centered on the organizations for the aliens, something that while isn't the most original thing, was different from the other books she's not only written but from other YA novels that I know. It was a slow burn and I was more interested once the character of Blake showed up, but it was a fairly decent book. 
 I am definitely enjoying the series. I don't agree with the whole 'Daemon is a controlling douche' thing. That argument is getting so old, particularly since Katy isn't a mousy girl that bows down to everything people tell her. Short of her mother (who I find charming and very much like a real mom), she doesn't do what people tell her to do. In fact, when Daemon begs her not to (view spoiler)[train with Blake she refuses to back down and continues to do so. Frankly I think people are many times getting 'concern for someone's safety' and 'controlling' mixed up. I am very much a feminist, but give it a rest. If women are going to get up in arms each time their significant other asks her not to disregard her safety, I think that just makes us a bunch of assholes. 
 And I mean that in more than just this book. I don't need an alpha male telling me what to do, but if he told me he didn't want me to do something because it could get me killed, I'd at least listen to him. 
 I'm still bothered by a lot of this though. I also wonder if my love for her other books is hindering my ability to make a rational judgement. I wish I read this series before I read her later works. (hide spoiler)]