I picked up this book based on the the short description on the back. I enjoy thrillers and realistic science fiction, so I figured that I would enjoy this book as well. And for the most part, I did. I really liked Rosie as a character and how she didn't pretend that she was like the other students, particularly the popular ones. I also enjoyed how she cared more about others than herself, though that sometimes got her into some trouble with trying to figure out her relationships with Linus, Burnham, and the other students, especially as she continued to discover more and more about the secrets of the school. Some of her choices I didn't quite understand. There is one in particular, toward the end of the book, where she trusted a complete stranger over a friend. I didn't understand why she thought that would be a good idea.
O'Brien's way of writing was pleasant to read and kept my attention, causing me to become invested in the characters. There were some annoyances though. One such annoyance was her overuse of “I said”/”He said”/etc. When reading a conversation between two people, the inclusion of the saying tags isn't always necessary and, sometimes, even distracts from the conversation. The biggest annoyance was the ending of the book. I had to re-read the last chapter to figure out exactly what happened. It didn't make me throw the book across the room as O'Brien said it made other readers (as stated in her interview included in my copy of the book). However, it didn't feel like a satisfactory ending. To be honest, I would have preferred the original ending she mentioned in the interview.
Overall, I liked The Vault of Dreamers, but the ending did not leave me feeling fulfilled, but rather like “Oh, that's it? It's done? Shrugs Okay, I guess.” And while I know there is a sequel, the ending seemed pretty finite and hasn't made me what to find out what happens next.