Some of the newer convenience features include the option to move more quickly around town using the 'jog' toggle found in the options menu, a spell that highlights objects lying on the floor as though the cursor was placed over them, and a spell that teleports the player to the nearest exit found on that level of the dungeon.

The difficulty of Hellfire dungeon floors 1-8 are is comparable to that of levels 9-16 of the main Diablo quest, requiring experienced characters to explore. The Hellfire dungeons are populated with new enemies that do not appear in the main Diablo quest, however. It should be noted, however, that there are almost no unique monsters found within Hellfire's exclusive dungeons. The new unique monsters, which appear as palette-swaps of normal monsters with unique names, also integrate in the main Diablo quest. New shrines are found where shrines would normally be found. Objects like oils, new weapons, rings and armor, and runes drop amid other more common kinds of items, and the new spellbooks, including books for two previously existing spells that did not have books, and scrolls are found in the same kinds of places. The rest of the expansion integrates more fully into the main adventure. However, if the player speaks to Lester before reaching either character level 15 or the Caves portion of the main quest, he will be hesitant to ask them to enter the new dungeons. In order to gain access to the dungeons, the player must speak with Lester the Farmer, who is north of Tristram, near the herd of cows. Hellfire integrates into Diablo, and because of its design, its new quests and dungeons do not have to be tackled to complete the original quest to slay Diablo. The expansion pack adds several enhancements to Diablo, including an additional Monk class, two new dungeon settings – namely The Festering Nest and the Demon Crypts – additional quests to undertake, several extra game items – including oils which affect item statistics and runes that can be placed as traps – a new page of spells, new affixes for weapons and armor, new shrines, new mini-boss enemy names, a noticeable boost to Diablo's strength and power, and a number of interface improvements. The player is later tasked with venturing into Na-Krul's lair and vanquishing it. A Sorcerer, while performing a ritual, inadvertently unleashes the demon Na-Krul upon the town of Tristram, but before it can completely escape, the Sorcerer magically seals the doors.

Hellfire's storyline occurs in parallel to the main story arc of the original game.

Diablo 3 immortal throne room