Dexter hasn't been worth a crap since the season of the Trinity Killer. That season was magnificent. Dexter jumped a mile over the shark immediately after that.
I'm just watching now out of curiosity to see how they wind up the series. Before Dexter jumped the shark I used to watch each episode 2 or 3 times, and I couldn't wait until Sunday night for the next episode. It's sad, but it's how most shows end.