Eh, I've learned to take a more relaxed approach to trailers like this.
See, there's two things that can happen:
1. The game turns out good. Yay! We've got a good game that's worth our money and an awesome trailer to top it off!
2. The game turns out bad. Yay! We've gotten to enjoy a completely free awesome trailer!
Either way, I profit. And all it requires for me to do so is to have a basic measure of patience to look into gameplay footage, trusted reviews etc. before buying if I decide I want it.
Ickabod said:
Seriously a portal from the sky, wouldn't the obvious choice be an Oblivion gate?
Oblivion gates are Mehrunes Dagon's thing. They're made of fire and earth because Mehrunes' associated with fire and earthquakes, things that cause widespread destruction and change. Which is his thing.
These portals are from Molag Bal. Enslavement and Domination are his thing, he's the King of Rape after all. Hence the chains and such. It's presumably coming from the sky as Molag Bal's plane of oblivion, Coldharbour, is a copy of Nirn (the world) except completely desecrated. So you know, his portals are in a mirrored position.