If you don't have RDR and are on the fence; go for it!
Bought this at some point near release for $60 and absolutely loved it (the only game I've ever cared enough for to 100% it).
Also Undead Nightmare is a fantastic DLC itself too. It took me 12 hours to beat and 100% ; and 4 hours were spent pretty much blindly exploring and admiring the scenery.
It's not "GTA with horses" as many people like to claim, in fact I'm not a huge fan of GTA and absolutely loved this game.