Red dead redemption main story is probably Rockstar's greatest game made to date, a lazy comparison would be simply to call it GTA in the wild west. The ending is one of the best I have witnessed and evokes genuine emotion.
The undead nightmare campaign unfortunately is extemely poor by comparison, it feels rushed and the missions get repetitive instantly so it becomes more of a chore to finish the story.
The strength of the main game and online is what gives this the deserved 5 star rating.