I found this randomly at B&N; it seemed promising. The beginning was close to 5 stars, with the expected action and violence and deadly characters. My enjoyment wavered over time, however. I didn't expect this book to be deep (it wasn't), but I expected good action scenes and better/cooler characterization. The action scenes simply weren't that great, and Koko herself started to feel a little unreal to me. She's also not a very sympathetic character, apparently feeling nothing after being responsible for the deaths of innocent people around her (which was also inconsistent with her views at other times).
The writing in this one was fine, but the characters weren't tested nearly enough. Sure, they were in physical danger at times, but Koko always seemed to get out of it quickly and far more efficiently than her enemies, and I never believed she was in any real danger. She had no novel solutions to problems either; it was always just: shoot them first, or fight better than they do. The enemies seemed deadly when introduced but came off more like pushovers when fighting Koko.
There is a big difference between an "okay" book and a "great" book. There wasn't enough tension, characterization, well-written action, depth, twists, or coolness factor to push this toward five stars.