Any of the 'good' endings were just never going to happen...you really think an American TV show is going to end with a cop letting a serial killer go loose...besides, Harrison totally had a point; Dexter killed bad guys because it was an excuse in the Code, not because he actually cared all that much.
The ending was pretty sloppy, it just felt rushed. I mean, the irony of 'saving' Harrison by having him actually kill someone was...what were they thinking? I was thinking maybe Dexter was going to give Angela a chance with the Matt Caldwell case, but would give her Kurt's bunker in exchange for forgetting the BHB stuff, but I guess they wanted to end it definitively.