If Naruto was evil, then I don't think hat he will be as strong as he is now, his strength increases with the more love in his heart, he is the opposite of Sasuke which get his strength from his hatred.
In the last chapter Minato stated that he has big present for Naruto, could it be the other half of Kurama's chakra? any other thoughts?
http://narutobase.net/manga/Naruto/627/16