After the First Battle of Hoover Dam, Caesar sent Ulysses to Great Salt Lake to rally the White Legs to destroy New Canaan. With his help, the White Legs found a large supply of weapons. The White Legs then destroyed New Canaan, sending Joshua Graham, the Burned Man, and the New Canaanites to the Zion Canyon, where the Dead Horses stand with them against Caesar. The Courier then arrives in the Zion Canyon and meets the Burned Man, Joshua Graham, who is surprised that it is a different Courier than Ulysses that came to him, as he had figured Ulysses would come to murder him. This sparks the beginning of Honest Hearts.
Honest Hearts takes you on an expedition to the unspoiled wilderness of Utah’s Zion National Park. Things go horribly wrong when your caravan is ambushed by a White Legs raiding band. As you try to find a way back to the Mojave, you become embroiled in a war between tribes and a conflict between a New Canaanite missionary and the mysterious Burned Man. The decisions you make will determine the fate of Zion.
The Honest Hearts add-on adds new crafting recipes to the game that make use of the Survival skill. Unlike recipes added by the previous add-on, Dead Money, most recipes added by Honest Hearts do not require add-on-specific items or perks. Most recipes are available from the start of the game, provided the player has the necessary skill level and ingredients.
The XP that is rewarded for quests is variable depending upon your level when the quests are completed. The total XP split between the main storyline quests is approximately 3000 XP at levels 1-4 and 22000 XP at levels 45-50, the secondary quest XP ranges from 75 XP per quest to 550 XP per quest.
Like Dead Money, you are not allowed to take companions with you into Zion. However, unlike Dead Money, Honest Hearts does not force them out of your party, you must do this yourself if you wish to proceed.
Honest Hearts, like all add-ons, raises the level cap by 5.
Equipment is not taken from the player at the beginning of the add-on, however the maximum weight limit is decreased due to the length of the journey. 100 pounds of equipment can be taken if you have the Strong Back or Pack Rat perks, and have a minimal Survival skill of 50, or pass the Speech check when talking to Jed Masterson, or Barter check (50) when talking to Ricky. Without these perks/skill levels, you will have a weight limit of 75.
The player is able to return to Zion after completing the add-on, however followers still cannot accompany you. They also cannot be left waiting at the Northern passage, and instead will return to their home (ED-E back to Primm, etc.). This is due to the 14 day length of the trip into Zion.
Honest Hearts features weather, adding rain/overcast to the game.
It's important to note that after completion of the add-on, most unique non-player characters will have left Zion.
If you choose to defeat the White Legs and allow the Dead Horses and Sorrows tribes to remain in Zion, after the main quest is finished, Dead Horses and Sorrows tribe members will still be at their respective camps and are peaceful to the Courier.
After the main quest is finished, Dead Horses and Sorrows tribe members can be killed for loot without receiving negative Karma. If you are seen attacking a Dead Horse, the entire tribe becomes permanently hostile.
As with Dead Money, there are no noticeable repercussions in the Mojave for your actions in Zion. This frees your normally "good" or "bad" character to complete quests in ways they usually wouldn't without affecting the Mojave.
The only merchant in Honest Hearts is Joshua Graham (Passing a speech check will allow you to purchase medical supplies from Daniel, however his caps and items are limited).
Many tribals are well-equipped, you can find some weapons that are rare in the Mojave Wasteland.
You can take the Animal Friend perk to face fewer hostile creatures.
None of the vehicles in Zion will explode.
It is possible to pickpocket any main character, such as Joshua Graham, Daniel or Follows-Chalk while they are asleep. Regardless, you cannot pickpocket their unique weapons and apparel.
Honest Hearts was first hinted at via in-game graffiti, sparking speculation that it would be the next add-on. This speculation was seemingly confirmed when ZeniMax registered "Honest Hearts" as a trademark. The graffiti hinting at Honest Hearts refers to Joshua Graham, and New Canaan, which were originally to appear in Van Buren, Black Isle's canceled Fallout 3 project.
Honest Hearts was again hinted at in the game files of the Dead Moneyadd-on, with the inclusion of an unused snowglobe for Zion National Park, and further suggesting it would be the next DLC in line for release after Dead Money.