The story of Kenna, the powerless of the title, is narrated in first person, present, and that might be the root of some of the downsides of the book. I did find the villains and Rebel more likeable characters than Kenna, who treads the line between trying to be determined and independent and sometimes comes across as obnoxious. (I agree with a previous comment that life would be easier if the villains' names weren't so similar to each other). She also proclaims she's smart but misses a few clues throughout the story that she's evidently seen or heard as she's the only narrator we have. And her internal monologues don’t always illuminate the character or the story and can be sometime repetitive.
There is little description of how the world is outside of the team of heroes/villains who end up working together, or how things have come to where they are, and we don't know when the story is set. The story is intriguing, and it improves as it moves along, it is easy to read, and the overall message is positive, but perhaps a more diverse point of view would help.