It wasn't that bad. Rollo was almost right about Deb catching them. If they hadn't built towards Deb being sympathetic to Number 13's plight, I'd say that plot point was a total cop-out (not unlike Dexter not having to be the one to eliminate Doakes), but they've been building towards this ever since Deb saw the tapes. Therefore, I'm willing to believe that Deb would have done that.
Dexter letting Quinn off was interesting. Quinn obviously knows it was Dexter, though I don't imagine it will see much play next season. Quinn as The New Doakes never really made any sense, because if anybody on the force could see the use in Dexter running around offing bad guys, it'd be shady old Quinn.
I've accepted at this point that Dexter will be entertaining and better than most of the crap on TV, but not truly great again until the final season of the show. And they'll be making the show until either Showcase or Hall want out; given that Hall gets exec producer credit and Showcase gets sweet ratings out of it, I don't see either of these things happening soon.