Killing Agag and Children?

So what's the deal with hewing/hacking King Agag to pieces? And then the annihilation of women and children? Isn't this a bit gruesome and bloodthirsty? Samuel comes out covered in blood at the end of the chapter and God not only approved of this, but commanded it--how can this be? How do we reconcile this account with the teaching of Jesus in the New Testament to pray for and love your enemies?