So I'm going to disagree with most people (didn't read the last two pages, I'm fucking tired as I was going to go to bed, decided to finish off the last half of ep 9 or something and then had to finish the rest of the damn season lol) and say this was my favorite season yet. No other season of Dexter, as great as others were, had me going "OH SHIT!" and getting giddy as a fucking 12 year old finding his first porn about what was going to happen next. I'm tired as shit and I'm nearly jumping up and down in my seat still from this season, and I almost never react like that to shows, I'm almost always calm and composed about stuff, but couldn't do it with Dexter, it was too good.
As for the details:
I absolutely loved Lumen. Yes, at first she was annoying, but similar to Hope in FFXIII, she's got a fucking excuse. She's lived through essentially the worst thing anyone can do to someone else and has to keep living after it. Her life has been upside down for a long time now and was batshit crazy in the early times. She really grew on me and I absolutely loved seeing her character get stronger and get some good hits in defending herself.
That said, fuck her leaving. The ONLY bad thing about the finale was this fact. Her leaving is total fucking bullshit, made absolutely (almost) zero sense and was just plain out of place. I really hope she is brought back. The Nanny has something going on with her, maybe, but I'd have no issues with her getting written out to allow Lumen to take care of Harrison and Astor/Cody. It would solve a lot of issues, but I guess that's not good for the writers then. But you can always bring Astor/Cody back for good and have the kids always be asking for Dexter to give a similar effect as him having to come back because of the Nanny bitching.
Astor grew on me too, she was annoying last season/early this and I was very happy to see her go, but I can see her on the show on a more regular basis, honestly. I was really hoping that the "share something with her" was going to be "You know how Trinity was the guy who killed your mother? I killed that mother fucker."
Dexter said Cody grew a foot, but he didn't.
I was getting annoyed with the Batista/La Guarda storyline, but I really like how it was handled later in the season. Batista was the fucking man, he got the leash around her neck and got her in line. You are the man Batista. It's obvious now that this storyline was just "filler" for the mid-season as they escalated Dex's main story. And I like how they cycled it out towards the end to only do little things and allow more time to the really good stuff.
I was happy with Deb's choice. As much as I'd love to see Deb find out about Dex, I can totally see why she did what she did and I really liked the character growth, especially what she said to Quinn at the end.
Quinn I'm not certain about. I like his character, but I'm not 100% on what he thinks about Dex, whether he now "knows" about him, or if he's just giving Dex the blind benefit of the doubt that Deb gives him because he's in love.
And to an earlier post about Jordan Chase being a similar "threat" as Arthur Mitchell: Yeah, he was. Want to know why/how? Arthur Mitchell had the same burdens as Dexter has, he has to live a double life and has many responsibilities to other people. He has a family, a church life, etc. that ties him down and limits his time. Jordan Chase was a millionaire, he had free time and loads of money, he could do what he wanted when he wanted it, aside from his psycho-tendencies. Was Jordan Chase was badass at Trinity? No fucking way, was he as dangerous? I'd say he was.
I'm too tired to think of anymore. So yeah.