The Undead Nightmare DLC is not nearly as good as the regular game. It has shortcomeings that are not hard to miss.
1. The story isn't as good
2. Ammo is very scarce
3. Zombies can come out in areas where there's no cover in sight
4. overall, constant spawning of hords and hords of zombies wihich gang up on you and kill you instantly is just not fun, not fun at all.
I mean, when I first heard of a single player DLC for Red Dead Redemption called Undead Nightmare is gonna come out, I thought to myself, "Finally, a single player DLC for Red Dead Redemption is gonna come out. There's finally gonna be a single player DLC." I was really looking forward to Undead Nightmare, but when I finally played it, I realized my antipisipatation was for nothing. I was very Disapointed. I mean, this DLC is not that much fun for me. Ten zombies can spawn at one time and instantly kill you. That is just not fun. Also, they come out in the middle of nowhere and ther's no place where you can take cover, let's face it, you're screwed. Now, I just want to comment specifically on the ammo. You know, when I play the regular game, I never ever run out of ammo for any of my guns, not even once. I never even have to buy any. That's because you can loot the dead and get ammo from them and there are ammo crates all around the world, including in all of your safehouses that you can of course, get ammo from. However, in the Undead Nightmare DLC, you're lucky if you have any ammo left over after one zombie attack. You barely ever get anything by looting the dead and there are not nearly as many ammo crates around the world. You don't even get to loot the ammo cates untill you defended the town you're in from a zombie attack. So most of the time, you're just stuck with this stupid 2 by 4 which is lighted on fire which you might think is cool to kill zombies with, but it's no good when you use it to fight off and try to kill hords and hords of them which keep spawning over and over again So, I think the firery 2 by 4 is useless.
So in Closing, I think The Red Dead Redemption single player DLC Undead Nightmare is not nearly as good as the regular game. I say it's OK at best. If you want a game that has a good zombie mode in it, try Call Of Duty: Black Ops.