Hopefully people stop feeling like anything "dark" is an emo teenage vampire. I never got that vibe from the Dark Brotherhood but apparently I'm alone in that.
I agree there, I got a number of vibes from the Dark Brotherhood, but the "emo teenage vampire" stereotype was never one of them.
My problem with the Dark Brotherhood wasn't just that they were teenage devil worshipers, but that they were simply unbelievable. The Cheydinhall branch were just too cheerful to be taken seriously, with the voice actors totally failing at convincing me that these people were stone cold killers. Lucien Lachance was even worse. When I first heard him, I didn't think "Woah, this guy is evil", I thought "Woah, this voice actor really needs to take it down a notch"
So you're problem is with the voice actors not really pulling off the "stone cold killer" thing? That happens. Especially when they're voiced by the same voice actors who do the voices for other characters of their race in the game and don't try to disguise this... At least Lucien Lechance tried to sound different from a generic Imperial.
On the other hand, if they tried to do the "stone cold killer" thing it could easily come off as over the top, I think, and end up just seeming ridiculous.
But we've known the Dark Brotherhood was in Skyrim for some time, and that's nice, I wonder how they'll differ from past games in Skyrim, though, and I'm assuming they will, as it seems like the way the Dark Brotherhood is portrayed is always changing between games, although in Morrowind it's actually hard to be sure since they only appeared as enemies in Tribunal and there wasn't enough detail on their inner workings to really compare tham adequately to other games.