Warning: Spoilers
I played this a LONG time ago I think in 2010 or 2011 before I went online. It takes place in 1911, the last days of the wild west. It's pretty much GTA in the wild west but there's also an honor, morality system so don't go too crazy. If you do you can get a bandanna to protect your honor.
There's also horse's that act as cars but don't push them too hard or they'll buck you off. Kick you with they're hind legs that is. Even some poker games and it also has a online co-op DLC (Down Loadable Content) that's free if you want to play with others. As well as some other free downloads too. At least on the PSN as far as I know.
I didn't play much of the Undead Nightmare DLC because I played the game to the end. I'm just going to say near the ending you'll be shocked and think "That can't actually happen" but that was how the wild west was. Everyone was a swindler and only the quickest survived.