The kill of Jordan and the scene with Deb and Lumen/Dex separated by plastic were the only interesting and semi-unpredictable scenes in this lackluster finale.
We all knew (1) Libby would be discovered, (2) Quinn would be implicated, particularly by the blood spatter, (3) Jordan, Lumen, and Dex would all have to be in the same room at some point, (4) Jordan would have to die, most likely murdered, (5) Deb and Quinn would be resolved one way or the other, (6) Lumen would have to leave, and (7) Harrison’s birthday party would have to occur, and Rita’s kids (Aster in particular) left to reconcile with Dex.
Furthermore, given the formula for past seasons, it was pretty clear a lot of the resolutions would intertwine and rely on lucky coincidence to be resolved. That made things like Dex’s faking the blood report fairly predictable; of course Dexter would be instrumental in Quinn’s ultimate fate, it was only a question of which way he’d go. Exonerating Quinn is the neater solution story-wise because it’s closer to a reset than if, say, Quinn went to jail. Lumen leaving is another one–given the formula and the profile of the actress, Lumen either had to die or leave; letting her live is a first (considering what happened to Lila, Jimmy Smits, and Trinity), but her departure was handled extremely poorly–what was with having her ride the front of Dex’s boat “Titanic”-like, flashing him loving smiles? I half expected the writers were going to bump her off in an accident–which would have been preferable to her inexplicable change of heart the next morning. I wouldn’t be surprised if she showed up again next season; her character provides so much in the way of dramatic possibilities for Dexter that the writers would be fools to ignore it (or, worse, give Dexter another girlfriend–who could possible top Lumen?).
Given the above, there just wasn’t a lot of room for surprises. I was poetic justice to see the overly-confident Jordan get outsmarted, and I thought that was surprising and handled well. I’ll also say the writers played fairly and laid good groundwork (over several episodes) to make Deb’s ultimate actions believable. But there is an inherent problem with an approach that resembles a limiting series–if after year one she is, say X away from knowing his secret, then the next year it’s X/2, then X/4, and so on, the increments get smaller and smaller, meaning they’re less explosive as time goes on.
For next season, the only possible way things could progress is if some who already knows Dexter well finds out his secret–my guess is Aster.