I'm disappointed in you, 'Dexter.'
You've had this storyline that's gone under the radar, threading itself into Dexter's path since last season. A guy who maybe knows more about Dexter than meets the eye. A guy that Dexter can't/shouldn't just get rid of by killing because he hasn't killed anyone (we assume), and thus, doesn't fit the code.
As much as you want to try and claim that he was just a petty kid who was mad that Dex didn't like how video game, I don't believe it. Let's look at the timeline here....
S6:E4 is when Masuka learns that the hand is being sold online.
S6:E5 is when Louis is hired and tells Masuka that he cannot find who bought the hand (which, as we will learn later, is him).
S6:E7: Louis shows Jamie the video game.
S6:E9: Louis has Jamie over to his apartment and we see the arm in his possession.
S6:E10: Louis shows Dexter his video game and Dex tells him it's terrible.
S6:E11 Louis mails the hand.
So, sure, maybe Louis mailed the hand to Dexter because he was legitimately mad that Dex hated on his video game. But WHY did he buy the hand to begin with? WHY did he create a video game about serial killers, putting emphasis on the Bay Harbor Butcher and seek approval from Dexter? And WHY was he so obsessed with Dexter from the get-go (asking Jamie if Dexter was as cool at home as he was at work)?
The guy was creepily obsessed with Dexter from the beginning, and now, BAM, with a shot to the head from some thug, he's dead.
I remember when Louis' story first started to develop, I thought, "Oh man, this is it. This is going to be the guy that takes down Dexter Morgan. It won't be a ruthless killer, or the law. It will be someone smart. And someone Dex can't just get rid of because he doesn't fit his code."
And now? Now you've killed off this smart antagonist in favor of one that dresses up like a bull and kills women in a maze. Seriously?
PS. This blog post would not have been possible without the help of the extensive Dexter Wiki. Fellow TV addicts, I salute you.
Also, check out this post on Louis from CliqueClack. It's awesome.