http://www.kotaku.com.au/2010/07/red-dead-redemption-adding-zombies-multiplayer-poker-more/
Multiplayer poker and liars dice might be good for a bit of fun, new gang hideous will be good and the zombie mode sounds like it could be fun

When I think of features I'd like to see in RDR zombies ain't the first thing that springs to mind. I'm intrested to see how they do them and still keep the western feel of the game.

Zombies in RDR?
Seriously? Even in a western setting... I don't like the idea.

All I know is I am waiting for the 15th when we have Sales here to buy it. I just haven't decided yet if I am going to buy it for the 360 or PS3. Probably PS3.
And yes, the zombie DLC should be a must buy. :)