Figured I'd revive this.
Overall, I'm torn on this season. While there's been some undeniably fantastic acting and writing, there are (from what I can tell) some real problems with the show that lie beneath the surface.
The writing of the characters has, by and large, been top-notch all the way through this season. I especially appreciated Dexter's breakdown early on, and how they're showing a more nuanced side to Deb. She's not just the potty-mouthed tough-girl anymore (not that she ever was, really), and they're finally really starting to explore that better.
That said, the plotting of this season...well, it's got enough recycling in it to keep Greenpeace happy.
First and worst is the Quinn = Doakes thing. Seriously, I hope they drop this storyline because it's been done and done better. It also does not bode well for Deb and Quinn, or for Deb personally. Hell, this could be the mechanism taken to have the big reveal to Deb, and I think they're already dropping hints about this. Her saying things like "You and Harrison are the most important things to me. Period" suggest that she's gonna find out, and gonna protect him. I think that means Quinn will have to die, possibly at her hand.
I'm split on the notion of Julia Styles' character. On the one hand I appreciate how they're handling her. On the other, haven't we seen the damaged girlfriend/damaged protege storyline before already? How is fusing S2 and S3 into a single character new ground? That said, I like the notion of there being a ring of these guys that have to be taken out. I still think, however, that she'll end up just like the other two, on the pointy-end of Dexter's self-preserving knife. Alternatively, she might take the fall for him to help clear his name or somesuch. Still, it's seeming like familiar ground in some respects.
Honestly, while I'm ENJOYING the season, I think this ought to be the last one. I think they've taken the show as far as they can story-wise. They generally handle characters quite well. Dexter has grown and changed a fair amount, Deb has as well, and the side characters are more fleshed out. But the plotlines keep treading on the same general territory, and/or the same emotional beats. Quinn's storyline in particular is pretty much the same "Oh noes!! Will Dexter get caughteded?!" thing that they bring up every season. It's old hat now and it always rings hollow. It's less a question of WILL he get caught, but rather HOW he'll get out of it. I think it's high time they stopped playing that particular card. All it does is jade me (and I suspect the rest of the audience). I doubt anyone's on the edge of their seat as far as "Will he get caught?!" anymore.
Likewise, the whole "Can he have someone who knows his secret" thing is getting tiresome. Of course he can't. He ALWAYS has to kill them. The loony girlfriend, Miguel, etc. Short of Deb, I don't see how anyone else could walk the earth knowing what Dexter does. It's POSSIBLE they'll let Lumen survive this series, but I doubt Julia Styles is going to become a regular cast-member.
Oh, and the nanny, too. Not sure where they're going with her. Maria Doyle Kennedy is a great actress (you may remember her as Catherine of Aragon from The Tudors), but she's fast stepping in to the Rita role of "nagging obligation waiting at home." I really hope they don't pursue that further, but she's been featured prominently enough that I think they'll do that. And again, it's yet more recycling.
Now, again, none of this is to say that what's being done is being done poorly. Far from it. But it's all got a been-there-done-that quality to it, and I think that's a BAD thing for a show, especially a show as well written as Dexter. That leads shows to take "bold" moves which often stray radically from what's come before, but then without effective follow-up. Example: Rita's death. I thought that'd have FAR more of an impact on Dexter's personality than it did. Basically, we got one or two episodes of him being alternatingly shut-down completely, and a COMPLETE lunatic....but that's it. There doesn't seem to be as much long-term effect, and it's "back to the usual" for both Dexter and the writers, it seems. Each season since S2 they've done soemthing radical, only to lapse back into the familiar.
All of this is why I say I hope they go out on a high note with this season, rather than drag it out another season using the same old tired routine.
Side note: Much as I despise the "Doakes: The Return" plotline, the dude playing Quinn is phenomenal. The level of intensity he's bringing to the role, especially given what came before, is really impressive. He needs his own show. Not as this character, but I think he could easily be a lead player in some show. I expect we'll see more from him.