Not a bad finale, but it's high time they stop with the eternal game of footsie and move the ball off the mark. I would have ended the episode with something that reveals that Deb knew it was Dexter behind the curtain and she wasn't ready to confront him with it.
I also think they missed an opportunity to keep Lumen in the story next season and far from having her conveniently lose her dark passenger (in a psychologically unconvincing twist; trauma just doesn't vanish overnight like that), have her become crazier and crazier, until she's a threat to Dexter but can't admit it to herself, much less him. I don't believe that killing all the rapists would cure her magically like that.
The writers need to show some guts and make choices that change the story permanently. They're being too conservative for a show like this.