But in all seriousness the siege is awesome, one of the amazing things about The Elder Scrolls universe is that you can be a part of it and save the world from one of those guys who loves slaving people (Mehrunes Dagon, Molag Bal).
Plus in the video you get to see Lord Mannimarco managing his business, it is the guy at the top of the White Gold Tower (the big big tower).
That big thing in the sky are Dark Anchors to bridge Oblivion to Cyrodiil. I know Molag Bal and such are semi gods, but it would be great if they actually made some research to create these devices to bridge one plane to the other.
If you don't know anything about the Elder Scrolls universe that's ok since you can pick up any game and become a super hero in a matter of hours.