My problem with the last season or two was that this whole show was geared towards the eventual climax of everybody Dexter knew finding out what he really was. That's what I'm pretty sure everyone wanted to see - we got a glimpse of it with Deb (despite it being dealt with in a fucking stupid manner), and, at least for a bit, it was intriguing television. You know, for eight seasons they did their best to make us invest in characters like Masuka, Angel, Quinn and, to a lesser extent, Astor and Cody, and you'd at least hope there's some sort of pay off. How do these people, who have come to know and like Dexter, react when they find out he's a serial killer?
But at the end of the day, it was all for nothing - all these characters could easily have been replaced by other people without sideplots, and it wouldn't have detracted from the final arc which was a fucking love story.
It's such a shame, because for all its faults, the show was pretty good for the first four or so seasons. I think ultimately the writers robbed us of a satisfactory and actually interesting ending by deciding that Dexter ending up caught or executed was too obvious, so they had to go a different way. Sometimes the obvious ending is the best one, considering they laid the groundwork for it for about five years.