The Dexter series finale is many things at many different times. It's often boring, it's often predictable and it often seems like the "right" ending. So overall, it's an okay finish to a horrible season of a show that should have ended a long, long time ago.
Dexter winds up paying for his crimes -- but Deb, of course, pays for them the most. And what could have been an ambiguous ending (is Dexter truly done?) winds up still being an ambiguous ending. (What is Dexter thinking in those final moments?)