The Power of Six features the same successes as its predecessor: The premise of the book is interesting. The plot moves quickly and never drags. Unfortunately, the novel also suffers from the same shortcomings: The plot moves so quickly that it stifles any and all character development. Due to this, the characters are contrived and flat. They detract from the story and what could have been a fascinating YA novel. Since the characters are so flat and one-dimensional, the romance between John and Sarah - as well as the love triangle springing up with Six - feels forced. They can't have chemistry if they don't have personalities. 
 In short: interesting plot, but too-fast paced to be meaningful or memorable. I read this in college, so perhaps me being out of the demographic made me appreciate it less. I could see young YA readers enjoying this book more.