Really good episode. I'll go so far as to say that it was better than virtually any episode in S5 or 6. It felt fresh, with a genuine 'WTF happens now' feeling to it. Felt like a S2 episode, where twists to the show felt like they could seriously effect Dexter's life (rather than the "running in place" feel of S3, 5-6).
I'm glad they didn't draw out Deb discovering the tools/blood slides. It made sense that as soon as she realized something was genuinely wrong long-term with Dex, she went straight for his apartment and did a real search. She's a veteran cop, it *should* be that easy for her if she's focused.
Frankly though it also showed that S6 was basically a waste. They should have just had Deb find out about him helping Lumen. Her sitting on his kill would have more credibility that way.