But, him killing Hannah's dad changed the tone of the show for me, I always looked at Dexter as a crime fighter/vigilante. The major theme of the show was can Dexter have self control and not get caught. It was never about reaching a higher level of enlightenment.
Now, he is starting to look like a detached, crazed killer, especially since he realized he is crazy and Harry was just a coping mechanism. If he kills LaGuerta or Matthews, its over, Dexter will have to go down. So, he can end up like Vic Mackey, and look like a monster by the end of the show.