This is truly epic – a complete AU, telling the story of a world in which Red Skull used the Tesseract to re-write the future, helping the Nazis/Hydra to win and causing Tony to end up on the wrong side. Seriously, it’s amazing, especially since Steve (the only one who remembers the original history) works not only with some of the Avengers but also X-Men/Brotherhood mutants.
In addition to this final trailer, there’s a whole Youtube playlist of teasers and “tv spots”, including a Director’s Commentary. I would so totally read a proper novel-length fanfic version of this!
ETA: Changed the link to a backup upload of the vid, since the original had been deleted.