Harrison is always giving indirect spoilers... He made a lot of events predictable. Whenever he says something bad might happen, Dexter shrugs off and someone close to him dies (or almost). That happened numerous times.
Saxon somehow escaping from that chair after Dexter decided not to kill him was extremely predictable... it was like he hadn't learned anything with the Trinity episode.
That made zero sense.
Deb's death didn't work out well. One moment, it's all good, 5 minutes later, she will be on a vegetative state forever, if lucky.
You can't simply do that to the second most important character of a show...
And poor Harrison, the boy never gets to know anything. I really wanted to know whether he'd become a serial killer, just Dexter & Brian. He had seen Rita dying in similar circumstances, so that was expected accodring to she series logic. Maybe a scene of him holding a knife suggestively would do it.
They could make it somewhat open ended and leave the fans wondering for years, just like the producers did with the ending of Inception, but alas, they ended it in a very forgettable way.
Dexter and/or Hannah dying would make much more sense, I think.