I didn’t feel like the book was ever actually scary. Gory yes, but making you think about it after reading? Not really. The flashbacks were particularly annoying and often made what would happen next very predictable. The flashbacks also detracted from the story and authentic character building.
About a third of the book takes place in a flashback of the past in an attempt to explain the background and history more. The flashbacks, in general, felt more like attempts to extend the story longer rather than supplement it.
Finally, there were just too many characters, primarily due to the flashbacks. It made it harder to relate to the main characters since there was so much jumping around.
I did like the setting — an underground hotel is quite unique. But I felt like the setting went mostly to waste and could have been better utilized to build atmosphere.