I know a lot of people are going to look at this and say "Great, MORE zombies", but think this over. We've done zombies in the present (95% of zombie games), zombies in the future (Borderlands' Zombie Island of Dr. Ned), zombies in World War 2 (zombie modes in Call of Duty)... but how often have we gone further back? The Old West was already a functionally-lawless society in many places, so what do you do when the nearest form of law enforcement is a hundred miles away across trackless scrubland, everything between you and it craves your sweet delicious flesh, your only ranged weapons are single-action revolvers, lever-action rifles or bows and arrows, and the only automatic firearm you're likely to see has to be mounted on a wagon and operates by a crank? Naturally, you band together with others... but desperate people can do desperate things, and in an all-but-forgotten frontier town, nobody knows what sins you commit except you- and whoever you let live.
This has some potential, and though I don't own RDR, I'm interested to see what they do with this.