Vicious is a great exploration of good/evil, mainly the shades in between, of what happens when ordinary people get superpowers they don't know how to handle, and in the case of the main protagonists, what happens when you are already messed up to begin with.
I confess that I love reading books about despicable characters. The complexity of their stories and the careful handling it takes to make them compelling despite their faults is fascinating. Schwab did a great job with this one. I hope to read more of these characters soon.