Some random blathering about this book, since I've had requests for my thoughts...not a proper review.
As is alluded to in the final pages of the novel, Phineas is the only character - only human on earth, apparently, who doesn't create his enemies by projecting his shadow side outwards. In fact, Phineas does not even have a shadow - Gene functions as his shadow. Thus, neither of them are whole without each other. The tragedy is that the shadow ends up killing the "light" side: evil triumphs, light cannot survive in a world full of people whose "hearts" are defective. The dichotomy of peace vs. war parallels the struggle between Gene and Phineas, who represent the war inherent in every man between his self and his shadow. In Knowles' story, shadow wins every time.
Thus forms the thesis of this high school grade lit essay of mine! And I didn't even use Sparknotes ;)