You have waited patiently all week and here it is, the trailer for Red Dead Redemption Undead Nightmare.
Below is the word from Rockstar:

Check out the debut trailer for the Undead Nightmare Pack. Unleashed upon the world of Red Dead Redemption, the Undead Nightmare Pack will feature an entirely new mostly single-player campaign that follows John Marston as he tries to find a cure for the highly infectious zombie plague that has spread across the frontier.

In addition to this epic new single-player adventure, the Undead Nightmare Pack also features brand new gameplay mechanics, weapons, zombie animals, mythical creatures and even a brand new secret location. All this, plus some exciting new multiplayer details and much more to be revealed very soon.

The Trailer is below. Enjoy!