This actually has me worried. Isaac was probably the most compelling part of the season - here was an extremely interesting villain who was more than capable of matching wits with Dexter. He posed a serious, legitimate threat... and now he's gone, 3 episodes before the end.
That leaves us with Hannah and the new "Mystery Arsonist" plot they're building up (gee, I wonder if the wormy cop with an obvious secret is involved)... neither of which quite compare. We have LaGuerta's plotline, I guess, but... eh, LaGuerta...
I don't know. I've been really digging the season so far, but I'm afraid that without Isaac to keep things going, all that momentum is going to stall.