I loved early Dexter. And I loved Season Five, but that was it for me. I still watch it to this day. I just don't enjoy it like I did. They are ending it too late and I can't say I'm all that excited about the conclusion.
If you want to see how a series goes out on a high note just tune into Breaking Bad. Wow.
As for Dexter, I may take a crack at the books sometime soon.