Complaining the Dark Brotherhood door isn't mysterious and interesting because we already saw it in Oblivion is like complaining that there's no tension in the third Star Wars movie because we already know Anakin becomes Darth Vader. Let's critique things that are bad, instead of critiquing at random.
Well, they could change the Dark Brotherhood all around again. They changed considerably from Daggerfall to Morrowind to Oblivion. In Daggerfall they looked like a bunch of crazy cultists adorned in black, white and gold. In Morrowind they were made into steam-punk looking assassins (although I've yet to get into the Tribunal content detailing why they're after you). In Oblivion they got made into medieval looking assassins who got outsmarted by a single, psychopathic cretin who's ultimate plan was to stab a ghost in front of everyone.
Then again, going by the Morrowind to Oblivion transition, maybe it's best if they don't change it anymore.
I can't help but get excited for this game when I scroll through and everybody's biggest beef is that Khajiit don't have enough leg joints and there are loading screens between certain areas.
Can't really complain about stuff that ain't been talked about, and previewers aren't known for being critical. Although you've already managed to forget a few things like the iPod interface, axing attributes, or keeping weapons that'd be useful against a fucking dragon out of the game in favour of dual-wielding swords because it looks more booyah to their target audience.