This was a story full of twists and turns that held my attention until the very end. There were a few problems with it, however.
1. Aria was a somewhat passive person carried along by events, not a very strong character. She screwed up a lot, she dithered when she should have been making decisions, and she didn't show much leadership. I get that she was only 16 years old, but she seemed like a person that things happen to rather than a person who makes things happen. It was lucky she had friends with such useful skills or she'd have been dead several times over.
2. Toward the end of the book, especially, events were happening so fast that there was no time to assimilate, much less expand on, them before something else was thrown in. Hammerschmidt is out of control! No wait, one of the Regulators is in crisis! Student epidemic, is it poison? Need a cure! Wounded teacher! Disappearing boyfriend! Is that Aria's brother?? On and on and on.
3. Language and grammar problems. Please don't feel like I'm singling out this book (much), because these issues are common. Misused words here and there, thankfully not too many, but odd choices (a row of expletives, shakes his stylist, a verifiable museum, footage is decomposed), some meanings of which I couldn't figure out. Misspellings (accidently, teaming/teeming, loose/lose, etc.) and punctuation errors. Not everyone is bothered by this stuff, but I happen to be, and that's why I bring it up.
Bottom line: it was a good story, and I'd be interested to see how it all turns out. It could use another round of editing to clean it up a little more, though, and a little expansion of the plot, especially near the end. Edit: 3.5 stars, rounded up to 4 because although language was an issue for me, it isn't for a lot of people.
If this plot interests you, you may also want to check out Fear University. It has more of a fantastical element (beasties and magic), but it should appeal to the same young adult audience.