The concept of a sentient prison that is living and willful (not to mention likely insane) was even more intriguing. I felt the author executed its characterization with a deft skill. She didn't skimp on portraying the depths to which humanity can sink, but she didn't wallow in it needlessly. The two paralleling story lines eventually intertwined in a seamless show of skill. It took me a while to make up my mind, but by the end I sympathized with both of the main characters and wanted what they wanted.
The writing is clean and enthralling, and the pacing is snappy. For handling and connecting two different worlds and world-views in one book, I thought it was very well done. I was left eager to dig into its sequel.