Yeah I'm sad and surprised to see him go, too, at least with this many episodes left. I'm not sure how I feel about the next big threat being randomly introduced this late.

Amusingly enough, right when Isaak was talking with his assistant about the two guys coming to kill him, I thought almost verbatim: "you know, Dexter would be a great ally right now if Isaak wanted to bury the hatchet." The very next scene, about 5 seconds later: Isaak knocked on Dexter's door.