Its called being a stuff dlc
Honest hearts in a nutshell: Your caravan gets ambushed by tribals and only you survive. Then you run into follows chalk who takes you to the burned man where he send you to do boring taskes and then sends you to another tribal camp where do more quests with a barely dressed woman with a bear claw. Then comes the final battle where you only fight for the burned man. The games ends based on what you decide to do Salt-upon wounds and what you say to your companions.
Dead Money: You are taken hostage and forced to do the bidding of a grumpy old man against his will and have to work with 3 other captives who
are soldiers of fortune and they are the a-team all have their own motives and personalities. You have limited supplies and you have to survive against the ghost people. Over time you are given the oppurtunity to save your fellow captives or kill them off one by one. After that you have a few options on how to deal with the old man. The game ends based on your actions with the captives and the old man.
In my opion buy both.